We wrote a small piece of software. Bare in mind that this was early 2000s and all we knew was some rudimentary Turbo Pascal 7. We would sit in front of the keyboard and have the pranked person next to us. We would tell them to ask a question to the program.
So we would run the program and the first prompt would have you type something along the lines of: "oh magic program, please answer this question for us". The program would say "Ask away...". You would type your question, hit enter and oh and behold! a reasonable answer to your question.
Needless to say, when we were "typing" the "oh magic program" quote, we were actually typing the answer to the question, but had rigged the output so that no matter what character we typed, it would always be that string. Thus the program "knew" the answer.
Funny thing is, this worked because of it's timing. This was an era where a lot of kids had grown up with a computer around the house, but many hadn't (third world country). So while it wasn't uncommon that some of us could type quickly and without looking at the keyboard, it wasn't the norm either. I'm sure kids nowadays would immediately catch up to the trick in no time. A handful of our classmates did.