Very interesting site that teaches you to make a fly powered match plane, but check out this chunk:

Catch a bunch of flies. Put them in a jar and put the jar in the freezer. In a few seconds the flies will be chilled out completely. This is called cryogenics, and it has its drawbacks. For example, the flies will be dead flies if you freeze them too long. Dead flies are no good. So if you're a tinkerer, refrigerate your flies. It takes longer to make them comatose, but they have a higher recovery rate than the ones you leave in the freezer next to the burritos.