In the popular multiplayer shooter
Team fortress 2 made by VALVe, you can choose a class named
spy, and that spy can turn himself invisible. So it is impossible to spot him and so there is a
pyro class which can set invisible spy on fire and make him visible for other clases
Engineer:"Ah man, it's a Spy 'round here!"
Pyro:"
SPYCHECK!! SPYCHECK!!" (turning around while holding trigger of
flamethrower)