Some of life's mysteries explained: Ten questions you never knew you wanted answered

Tomorrow, The New Scientist publishes a collection of 101 questions and answers provided by its readers for its 'Last Word' column, now in its 12th year. Cahal Milmo and Amol Rajan dip into a world stranger than fiction.

Does beheading hurt?

Yes. A medical study in 1983 concluded that no matter how efficient the method of execution, a few seconds of pain is inevitable when losing one's head. The guillotine, considered one of the more "humane" methods, relies on severing the brain and spinal cord after cutting the surrounding tissues. Even so, at least two to three seconds of intense pain cannot be avoided. There are many accounts of the heads of executed people continuing to show movement or expression long after the final blow. One particularly gruesome experiment in 1905 involved a French physician who called out the name of the condemned man in the seconds after decapitation. The response was for the eyelids over the severed head to slowly lift up and then the pupils focused on the doctor before then slowly closing again. The doctor claimed that when he repeated the dead man's name, the same actions took place. It was only at the third attempt that the head gave no response. The exact of amount of pain of course relies on the proficiency of the executioner. When Mary Queen of Scots was beheaded in 1587, the axeman took three attempts to sever the head and even then had to finish the job with a knife.

Why are pineapples so spiny?

The prickly exterior of a pineapple seems to contradict its very purpose: how on earth are seed- dispensing animals supposed to get to the sweet flesh inside? When it comes to pineapples - and bananas, for that matter - humans are very impatient. When sold commercially, pineapples are actually very far from ripe. Forest-dwelling creatures eat pineapples after they have ripened much more and fallen, usually from quite a height, to the forest floor. After lying there for a few days, the fruit becomes mushy and easy to open - which is how all the other animals get inside it. The prickly exterior is in fact a feature of many plants, designed to protect their fruits until they have fully ripened.

How big is the average mole tunnel network?

The mole eats worms and other creepy crawlies that enter its subterranean world. The size of its network depends on how rich the food supply is - a mole under a lush worm-rich meadow will need a smaller network than one that made its home in acidic soil. The area worked by an adult mole can stretch over 7,000 square metres, building a complex of tunnels with as many as six levels. The molehill is created by deep excavation to create a mixture of transit tunnels and "traps" to hold its prey.

Does wearing black make your bum look smaller?

Yes. The human eye can only perceive shapes if the object appears in different shades or colours. It is easier to notice wrinkles on a piece of light clothing than on a dark one. Thus in black clothing the shadows are barely discernible and the shape appears flat. The problem is that this only works when viewing directly from behind. When in profile, the backside will still reveal its true dimensions. The effect of shadows on the human face also explains why people of a darker complexion appear to age better than those with pale skin. Wrinkles are visible by the shadows they create and are therefore harder to see on dark skin.

Why do dock leaves relieve nettle stings so effectively?

The stinging nettle causes the discomfort so familiar to curious children and errant walkers by distributing a mixture of three chemicals when the delicate hairs on the leaves are broken by contact with the skin. The broadly acidic chemicals are countered by an alkali in the leaves of the broad-leafed dock, Rumex obtusifolia, which is released when the leaves are crushed and placed against the skin. Their effectiveness is none the less questionable, with some suggesting any comfort is more likely to be derived from the coolness of the leaf on irritated skin and their abundance close to nettle clumps.

How many species live on or in the human body?

The short answer is about 200, including 80 in the mouth alone. But that is to belie the sheer industry of the microbial entrepreneurs that inhabit our beings. The total number of bacteria excreted by the body every day ranges from 100 billion to 100 trillion. Every square centimetre of human bowel is home to around 10 billion microbes. Some 10 million organisms occupy every square centimetre of flesh. The most densely populated areas of the human body are the teeth, throat and alimentary tract, where the concentrations are increased by a thousand compared to bare skin. But while such figures seem huge, it has been calculated that the amount of bacteria on the skin of the average human would be the same size as a pea. That is to say nothing of the common parasites found on the human body. The follicle mite, found on every individual, spends its days harmlessly munching dead skin cells. Which is less than can be said for Naegleria fowleri, an amoeba that invades the brain and multiplies until the host drops dead.

Why does lemon juice stop apples turning brown?

The answer to this lies at the cellular level of the fruit. When a knife cuts the skin, the cells are ruptured and the air oxidises enzymes in the fruit, called polyphenol oxidases. This process creates the browning effect, designed to help any healing process and make the fruit unattractive to animals. Lemon counteracts this process in two ways. First, its high vitamin C content is a natural antioxidant that is turned into a colourless product rather than the apple or pear's phenolic compounds. Second, the citric acid in lemon slows down the browning process by dint of the lemon juice being more acidic than that of the apple.

How fat would you need to be to be bulletproof?

The short answer seems to be dangerously obese. A 9mm bullet, the most common type used in a hand gun, is generally held to be able to penetrate 60cm of human flesh before it comes to a halt. In addition, the bullet will cause one cubic centimetre of damage to the surrounding tissue for every centimetre that it penetrates the body. The calculations are based on firing a bullet into gelatine of the same consistency as human flesh and so do not allow for the fact that the projectile can be stopped by bone or simply pass through the body. Even if the bullet were to be stopped by body fat, the shock wave of the impact is likely seriously to damage internal organs. In the event of a person having enough girth to absorb a bullet, they are likely to drop dead from a coronary before getting shot.

Does anything eat wasps?

Yes. Quite a few creatures are fond of munching on this creature sent to spoil picnics. Birds, skunks, bears, badgers, bats, weasels, rats and mice are all partial to them. The bee eater, one of 133 birds that include the wasp in their diet, counteracts the sting by rubbing the insect forcefully against a branch or tree trunk. Badgers have also been known to dig out a wasps' nest and consume it, impervious to the displeasure of its owners. Dragonflies, frogs, moths and beetles are also known "vespivores". The larvae of several wasp species are also said to taste good when fried in butter.

How much surface area of the UK is taken up by roads?

Despite the fact that roads take up more space than any other type of land use in London, apart from gardens, the asphalt jungle is significantly smaller than some might imagine - accounting for less than 1 per cent of the UK's surface area. Road enthusiasts have calculated that there are 425,000km (264,000 miles) of public road in Britain (including 3,590km of motorway and nearly 57,000km of A road). Working on the basis that road widths range from an average of 26m for motorways to 3m for the 242,000km of unclassified road, that equates to 2,200sq km of road. Compared with the surface area of the UK, some 241,000sq km, this equates to 0.9 per cent of the total. The official government figure is 3,300sq km of road (1.4 per cent of total land area), but this includes verges and hedgerows.

Why didn't nature invent the wheel?

It did, only we didn't notice until fairly recently. Nature uses round discs to move around at a microscopic level. Bacteria use "wheels" to get around; they employ what is known as bacterium flagellum, a rotating mechanism that drives them along. Half of all known bacteria have at least one flagellum, which works by attaching itself to a "wheel" in the cell membrane. This wheel generates electricity by rotating at huge speeds (up to 100 times per second), and causing fluctuating charges in a ring of proteins that is attached to the cell membrane. Sounds sophisticated, because it is - and bacteria got there first.