And they know when they are in trouble!  My one dog got a hold of my glasses (my fault for letting them within his reach).  I walked in the house and he greets me with his usual exuberance.  I see something on the floor and say out loud "What is this?"  I mean, I didn't yell or anything because it didn't register yet what I was looking at.  As soon as I said it his tail went down and he went over and cowered in his dog bed.  He knew,  that little SOB knew..........!