Back in my youth I was trout fishing one evening on the Pine River in central WI waiting for a mayfly hatch to occur.  I was standing still in mid stream just as it was getting dusk and I noticed a ripple in the water right next to me.  When I looked down a big beaver did a KA PLUNK with it's tail.   I was out of that river in about two seconds flat.  Scared the living crap out of me.  I had never seen a beaver in the wild prior to that.

Fast forward fifty years and on a pleasant note.  I was standing in the woods along the shore of Red Lake and a bunch of beavers were hauling branches back and forth fairly close to shore.   I stood perfectly still and as they passed I could hear them making  "mumuring" sounds of some sort.  I watched and listened to them for about an hour.  I never looked it up but I'm assuming they were communicating with each other.  That was a neat experience.