Oh my god, this happened just a month ago. I know this startles a lot of people, but there's at least somewhat of a story here:
At Disneyland, riding Thunder Mountain, assuming it's going to be just another coaster through a rocky landscape (I had never been on a Disney coaster before). It's night time and I can only see what's purposely lit up, which makes this worse. Well (you guys probably all know this) there's a part where you go by a couple wolves and a possum is hanging on a branch above you. I saw the possum, but didn't see the baby possums that are spinning around until the last second!! literally thought it was some piece of debris heading for my face, so I jumped from being startled and somehow bonked my girlfriend in the head (:( I feel so bad for that still)
Well she had no clue why I jumped and whacked her head, so we decided to ride it again and this time I was going to point it out. I didn't tell her what it was, I just said to look up at something moving next to the hanging possum. We get to that part of the ride, I scream and point "there!" and she sees it just as they swing around the pole. She screams and jumps out of her seat louder and farther than I have ever seen her do before!
Needless to say, those stupid baby possums scared the living crap out of both of us, on separate occasions!