Back when I was a lot younger, a friend of mine and I used to have typing competitions on any computer that we came across (usually at school). The challenge? To type 'the cat sat on the mat' as fast as possible.
One day we were playing a game called Free Fall on my old BBC back home, and my friend, by habit, started typing 'the cat sat on the mat' while waiting for it to load.
He was still typing it when he got into the game, and when the first enemy emerged on the screen, it spontaneously blew up. We absolutely freaked at this point, and he carried on typing it - 'the cat sat on the mat'. More and more enemies were blowing up. The mat-lounging feline held the secret to the ultimate cheat! We were geniuses!
Turns out that the explanation for this was a lot more simple - someone had coded the cheat into the game so that if you simply pressed 'e' on the keyboard then it would cause all enemies on the screen to be wiped out. This was not documented anywhere, and I'd been playing the game for a good few years without ever discovering it. I'll never forget our reaction when it first happened, though - good times.