My pit lab mix had certain pit traits. He had a wide mouth and a very deep chest. He loved stuffed animals and would give them what we called "the pit bull shake" when he played with them. Also, pits seem to gravitate toward each other (weird...I don't know why) so if you take him to a dog park he will usually want to run with other pits. Don't worry about "pit" issues. Both pits and labs are intelligent dogs and if he is raised in a good home he can be a great dog!
