"The Babel fish is a small, yellow and leech-like, and probably the oddest thing in the Universe. It feeds on brainwave energy recieved not from its own carrier but from the aroung it. It absorbs all unconscious mental frequencies from this brainwave energy to nourish itself with."
"The practical upshot of all this is that if you stick a Babel fish in your ear you can instantly understand anything said to you in any form of language."