When I was young, a friend and I set up ELIZA in BASIC on a TS2068. It was fun, for sure. About an hour in, it responded with "i am" - lower case, when everything we'd put in was in upper case.
This freaked us the fuck out for about a half hour.
Then I realized ... wait a minute. Everything it can possibly say is in the code somewhere. I pored over all the things we'd put in, and finally, there it was: "i am". The only mystery that still remains is how that got there.