Good Questions: Why it's funnier to be tickled by the one you love

TICKLING, tea, tail-wagging and bumbags have been troubling readers this week. We hope the following will help.

Why is it that you can't tickle yourself? (Paul Roberts, Camberley, Surrey)

This question was once put to a BBC Brains Trust when the panel, after some embarrassed giggling, could do no better than describe it as one of the insoluble mysteries of human nature. A good answer, however, has been provided by Arthur Koestler as part of a discussion of the similarities between creativity and humour.

At the heart of both processes, he maintains, is the process he refers to as 'bisociation' - perceiving something in two self-consistent but habitually incompatible frames of reference. Creativity involves finding a new way to link old concepts; most jokes involve a build- up of expectancy which is dashed by the punchline. In each case, there is bisociation demanding the resolution of two apparently incompatible interpretations.

Tickling involves a mock attack designed to provoke laughter. It is only funny if perceived as such. Tickling experiments on babies less than one year old have shown that they are considerably more likely to laugh when tickled by their mothers than by a stranger. The baby can only be certain it is a mock attack if the tickler is trusted. Koestler says the rule of the game is as follows: 'Let me be just a little frightened so that I can enjoy the relief.'

When a stranger tickles, the baby cannot be certain that the attack is not genuine. When you try to tickle yourself, it is the aspect of slight apprehensiveness that is lacking, so you cannot bisociate and you don't laugh. Koestler's theory is supported by a study conducted in 1980 of different types of laughter. People laugh for four reasons: tension-release, social, humour, or tickling. By provoking and recording all four types, asking people to guess which were which, and playing the sounds through a spectral analyser, the research showed that tickling-laughter is similar to humour-laughter, while social laughter and tension-release laughter are also hard to distinguish from each other though different from the other two types.

Sources: 'The Act of Creation' (A Koestler); 'The Perception of Laughter and its Acoustical Properties' (P A Mitford, PhD thesis).

Why do people fill the kettle with cold water when it would be both quicker and save energy to fill it from the hot tap? It cannot be to do with the purity or safety of the water, surely, because boiled water is purified by that process, from whichever tap it originates. (Julian Ogilvie, Hammersmith, London)

Both Thames Water and Lee Valley Water agree that water from the hot tap is probably safe when boiled, but they both advise against it. Cold water comes directly from the mains, coming into contact only with fittings that have to conform to certain regulations.

Hot water is not under the same restrictions and may have come into contact with potentially contaminating agents in the pipes or storage system of the water heating system. 'By and large, there's not going to be that much difference,' said the spokesman from Thames Water, 'but your tea won't taste as good from the hot tap.'

Why does tail-wagging signify pleasure in a dog but anger in a cat? (R J A Adams, Oakham, Rutland)

The whole question of physical manifestation of emotional states, in both humans and animals, is under-explored and extremely complex. In other words, we don't know. But we do know that the question is much more complicated than expressed above.

Dogs wag their tails mostly as a greeting, or when approaching someone they know well or with whom they have a good relationship, but tail-wagging extends through a range of emotional states, not all happy. Just as humans may smile wryly when things go wrong, a dog may wag its tail unhappily too.

Cats wag their tails when they find something really interesting. In general, in both animals it is a sign of a heightened emotional state.

Ferrets, incidentally, wag their tails when meeting another ferret head on.

To investigate the role of tail- wagging properly, one would have to go back a very long time in evolution. Originally, it must have been linked to the locomotor movements of the spinal cord. For many lizards, the tail plays an important part in motion. Somewhere along the evolutionary line, tail- twitching became detached from having a purely locomotor role and became part of a general exhibition of excitement, then perhaps of communication.

To provide a general theory of tail-wagging in cats and dogs, we would need firstly a classification system for human emotions (on which some degree of progress has been made), then more work on the role of the tail in different carnivores.

The final question, of the extent to which animals and humans can be said to share the same emotions, may be impossible to answer. It is, however, generally believed that most domestic pets regard their owners as members of their own species.

Principal source: Prof Richard Andrew, Sussex University.

And finally, though we must apologise for having mislaid the name of the reader who submitted this question:

Why do they call them bumbags, when most people wear them at the front?

The object in question first appeared in 1971 in American catalogues of accessories for back-packers, cyclists and skiers, and was known as the 'fanny-pack'.

They spread to more general use in the late 1980s, and in 1988 the Atlanta Journal reported: 'On New York's subways, the zippered waist pack is an everyday way for young people to safeguard wallets and other valuables . . . When these packs are advertised in catalogs for hikers or bikers, they are called 'fanny-packs' and are intended for wear in the back, but the subway riders turn them to the front, so they are in a visible, clutchable position.'

When fanny-packs came to Europe, also in the late 1980s, comparable terms appeared in various languages. The word 'bumbag' appears in the 1991 edition of Brewer's 20th Century Phrase & Fable, and in the 1993 Shorter Oxford Dictionary. In Norway, the correct term is rumptaske.

Compiled by William Hartston