Ghost from the Past

Since Colin is a rescue dog, I keep looking for strange behaviors resulting from conditions in his life before he came to us. He is amazingly well adjusted. The only unusual behavior that I've observed is his reluctance to step out of his crate. He is always excited to see us when we approach him in the crate - in the morning after sleeping all night or in the crate in the van. We open the crate door and he wiggles with excitement and wants to be petted. However he never pushes to get out and even when I move back to give him room and tell him it is OK to come out he still hesitates and only very timidly steps out. If I reach in to pick him up, he will back away from me. This reaction from a dog who in all other circumstances is fearless (to the point of being almost reckless) and begs for petting from us and just about anyone else he meets. I'm guessing he spent most of his time in a create and was punished in some way if he ever attempted to get out. If this is the only issue he is bringing to us, we are very fortunate!