Is it dangerous to swallow chewing gum? If you swallow chewing gum, it is normally excreted in the usual way, and should not be a health hazard. However, if you choke on your chewing gum and it enters the respiratory tract, this can be a serious matter. Such accidents typically occur during contact sports like rugby. If the gum lodges in the bronchi, wheezing and infection result. If it sticks in the trachea, fatal asphyxia can ensue. Therefore chewing gum during these activities is highly inadvisable. How did the colour red come to be associated with danger and the colour green with safety? One can only speculate on the origin of this universal code. A possible explanation is that the colour of blood of most living creatures is red; therefore red has come to be associated with danger. Green, on the other hand, has long symbolised hope, fertility and nature. Does the symbol have a name? In English, the symbol is boringly known as 'commercial at', but other languages offer more imaginative names. In Swedish, it is called snabel - a with an elephant's trunk - or kanelbulle, the Swedish equivalent of the Chelsea bun. In German it is called klammerraffe - a clinging monkey, presumably hanging from the tree by an arm. In Dutch it is called apestaart, which means a monkey's tail, probably because it looks like a monkey with his tail curled over him. In today's computer language, means 'at' and is used in reference to an e-mail address. Why are most opera singers fat? This is a popular illusion. In fact, there are many examples of slim singers - Maria Callas springs to mind. It is true there is still a belief among singers that an essential part of developing a powerful voice is to feed it. Fat certainly used to be seen as strength in musical worlds (making you a better player, especially for people like brass players). It could simply be that different standards of physical beauty, combined with an attitude that sound and ability is more important than appearance, have led to the tradition of many opera singers being on the plump side. Why does eating certain foods, such as asparagus, make your urine smell? Asparagus is made up of a group of naturally-occurring, sulphur-containing compounds, the most important of which has been named asparagusic acid. When these sulphur compounds are broken down in the body during digestion, a number of sulphur-related chemicals are formed. Together these produce the odour which some people can detect in their urine. However, the intensity of the smell will depend on the metabolic rate and hormonal levels of each person.