jargon /hi:'zen-buhg/ (From Heisenberg's Uncertainty

Principle in quantum physics) A bug that disappears or alters

its behaviour when one attempts to probe or isolate it. (This

usage is not even particularly fanciful; the use of a debugger

sometimes alters a program's operating environment

significantly enough that buggy code, such as that which

relies on the values of uninitialised memory, behaves quite

differently.)