Why does my dog cry when he carries his favorite toy?

My 8 year old Am Staff / Lab mix got a squeaky plastic monkey from a family member for Christmas. We expected it to last 5 minutes before being torn to shreds. Instead he carries it everywhere. He licks it sometimes but never chews on it. Occasionally pushes down on it gently to make it squeak. It's adorable but a little perplexing. Especially when he walks around the room carrying it and making a high pitched whining sound. At first we were worried he was scared, but that doesn't seem to be it. Does anyone else have a dog that does something like this?

He thinks it's a puppy, and yet it doesn't move by itself. I would try him with a toy that doesn't have a squeaker, and see if that makes him a bit more calm. The squeaking may make him think it's a puppy that is in trouble, and the whining is him being anxious about it.

I had a female dog that did this when she had ovarian cyst. if the dog never acted like this before their could be a hormone problem the vet can diagnose and treat.