ha ha, amazing. Seeing different (potentially harmful) things is fun. For me, deep water soloing (climbing about the sea then jumping off) in Thailand was one - getting about 10 meters up, just about to jump off and spot 2 sea snakes below. I tried to climb around but fell anyway. Or swimming above a stingray then noticing it whilst pretty much on top of it - luckily it didn't Steve Irwin me
The snakes and spiders in Thailand scared the life out of me, saw 2 or 3 daily. We think we have big spiders here

I chased a stingray around for a while in Fiji, made sure there was a good few feet of water between us all the time though, Irwin was prominently in my mind.