I grew up in Florida and our house was right next to a small lake. We had dogs and so our back door had a dogdoor on it so they could go in and out. That door lead right into the laundry room which wasn't air conditioned. We had another door between the laundry room and the actual house that we only kept open if the A/C was off and we were home (picture a man-trap where the outer door has a dogdoor in it and there's a washer/dryer in the trap).

Anyways one day when I was 9 or 10 I'm home alone, I think my parents had just gone shopping or something and I just wanted to stay home playing video games. I hear some weird thumping noises coming from the back door so I figure one of the dogs might have gotten left outside when my parents left and went to let them in.

I start to open the door without even looking, but by habit I look down at the laundry room floor through the glass on the door and see a *fucking alligator* curled up in the laundry room. And of course I bump it with the door and it immediately hisses at me. I yanked the door back towards me to close it, flipped the lock, and sprinted back into my room.

It kinda bumped around in there for a bit until my parents got back. I dunno if it just couldn't figure out how to get back out the dogdoor or if it thought there was something it wanted in there, but once my dad opened the back door and poked at it with a rake for a bit it just kinda ran off no harm done. It was only 4 or 5 feet long but as a small child it scared the shit out of me.