Most software errors are edge cases, like when a program receives an input from a user that the programmer didn’t account for.

The software tester is “fuzzing” the input function of the bar by throwing a bunch of weird inputs at it, like jumping through the door rather than walking or ordering absurd, negative, or non-numerical quantities of beer. This is a common way of testing software to make sure it won’t crash and burn if unexpected things happen.

Satisfied that the inputs for entering the bar and ordering beer are working properly, the bar opens, and the very first customer still manages to crash it by asking something entirely unrelated to ordering beer.