This phenomenon is called Arnold's ear-cough reflex. It occurs in about 2 per cent of the population and was first described in 1832 by Friedrich Arnold, professor of anatomy at Heidelberg University in Germany.

The vagus (Latin for "wanderer") nerve arises in the brain stem and provides a nerve supply to the external ear canal, larynx, heart, stomach and intestine. Stimulation of the auricular branch of the nerve by objects inserted into the ear canal causes a reflex stimulation of the laryngeal branches of the vagus, which produces the cough in susceptible people.

A variant of Arnold's reflex is vomiting caused by reflex stimulation of the vagal branches supplying the stomach. Wealthy Anglo-Saxons who enjoyed feasting are said to have poured cold water into the ear to produce vomiting when they had eaten their fill so that they could continue to indulge themselves - hence an alternative name for the auricular nerve: the alderman's nerve. The Romans are said to have achieved the same result during their orgies by tickling the ear canal with a feather.

Maurice Little, Maidstone, Kent, UK

This is one example of what are called neural reflexes. They are generally explained as the "confusion" of one nerve path (usually sensory) with another (usually motor). For example, rubbing the skin at the back of the neck produces a widening of the pupils, and scratching the inner skin of a man's thigh will result in the raising of the testicle within the scrotum on that side. This kind of information is used clinically to determine the integrity of a particular neural pathway. It can also be used to liven up otherwise dull parties.

Joseph F. Gennaro, University of Florida Medical Center, Gainesville, Florida, US

When scuba diving in the tropics a couple of years ago I had the sensation that something had entered my ear at high speed. I don't recall coughing but I was so shocked I spat out my mouthpiece.

I hastily replaced it and poked around in my ear to remove what had darted in there. When I saw the characteristic incandescent blue stripes of the bluestreak cleaner wrasse (Labroides dimidiatus), which cleans bigger fish for food, I assumed that I had just passed over one of its cleaning stations and been relieved of some earwax.

Mike Follows, Willenhall, West Midlands, UK