Scientific American.com: Ask the experts your science and technology questions SEARCH Advanced Search HOT LISTS: Readers' Favorites Best-Seller List Web Awards September 19, 2003 ADVERTISEMENT Current Questions What causes feedback in a guitar or microphone? How do you get a computer virus? Why do humans get "goosebumps" when they are cold, or under other circumstances? How do neon lights work? Questions by Subject: How do planets acquire rings? Why and how do planets rotate? Why do humans get "goosebumps" when they are cold, or under other circumstances? Why can't a person tickle himself? How do food manufacturers calculate the calorie count of packaged foods? How does a flame behave in zero gravity? EXCLUSIVE ONLINE ISSUES How do you get a computer virus? Forces of Nature Why do computers crash? HIV: 20 Years of Research Prehistoric Beasts What makes Kansas, Texas and Oklahoma so prone to tornadoes? Why do clouds turn gray before it rains? Tackling Major Killers: Heart Disease The Search for Alien Life What is quicksand? The Science of War: Nuclear History How do volcanoes affect world climate? The Future of the Web The Science of War: Weapons What is game theory and what are some of its applications? On average, how many degrees apart is any one person in the world from another? SPECIAL EDITIONS New Light on the Solar System New Look at Human Evolution The Edge of Physics What causes insomnia? The Once and Future Cosmos Do people lose their senses of smell and taste as they age? The Hidden Mind What causes feedback in a guitar or microphone? How do neon lights work? http://www.sciam.com/askexpert_directory.cfm (1 of 2)19/09/2003 22:48:20 Scientific American.com: As