Programmers created a bar and decided to test it. The tester enters the bar and starts ordering beer. He ordered 17 beers. Ordered 99999 beers. Ordered 0 beer. Ordered -1 beer. Ordered "duck" beer. Ordered NoN beer. Ordered 19.5732 beers. Everything works, you can call for customers.

The first real customer walks into the bar and asks where the restroom is. The bar catches fire, everyone dies