Let your dog know you want to play by getting down on your hands and knees and stretching out your arms and legs.
Cats are very smart animals, but they've never learned to take orders like dogs have.
Dog's wild relatives lived in packs that were run by a pack leader. Your dog thinks you are his pack leader, and wants naturally wants to obey and please you. Cats wild relatives lived on their own and and never learned to take orders from anyone. Worms don't have eyes, so they feel their way around. They move so slowly, though, that they don't hurt themselves when they bump into things.