I have had two scary experiences
One I was wading through a creek barefoot when I found some braid floating I grabbed it and it lead to right where I was standing, it turns out the "rock" my left foot was on was actually a snapping turtle. Needless to say I was up out of that creek quickly.
Two I was fishing a golf course in Florida when I caught about a one pounder. A 7 foot gator came flying out of the pond while I was bent over getting the hook out of the fish. I dropped the fish and my rod on the spot and booked it. The gator stopped and ate the fish but did not leave the area for about 15 minutes.