I was fly fishing a few years ago & my son starting yelling that there was a beaver swimming next to him in the river. I was like "sweet, what does he look like?" and then a few minutes latter this submarine like critter came cruising next to me leg up river, within inches of my thigh. He came up for air and started smacking his tail on the water several times & circling my position in the river. I later found out that this was a territorial warning thing. I felt lucky he didn't attack & now with this story I am even more thankful.
Critters in nature are out to survive, at all costs. You can't go running for cover with every sighting of every critter in the woods, but you surely need to be very smart and careful just the same...