They may just have two different speeds. Thor has always been more laid back the either of my girls. We had Star when we got Thor and they played together, but Thor always wimped after a short while. Later as Star was slowing down with age and arthritis, we got Arabella. Thor and Arabella got on great when she was a pup. Puppies would go for a short while and then need to nap. This really suited Thor. Arabella has however grown out of the nap times and would go non-stop 12 hours at a time if we let her. My two will play together for 1 or 2 twenty or sessions a day. Other than that it is upto my dh and me to entertain Arabella. Lets just say we go thru a lot of tennis balls.
Pam, Mom to
Thor-male brindle 05/24/01
Arabella-female brindle 12/19/06
Star-at the bridge 05/13/98-11/22/08