Sorry if this is a stupid question. My 15w old is fascinated by his hands (he loves staring at them and self-soothes by sucking on them. He also likes to swat at things that are dangling above him or in front of him. And he uses them in other normal ways like rubbing his eyes when he's tired. But he has no interest in holding anything, eg he doesn't want to hold or grab toys. He does hold onto people's fingers but not on his own initiative (and sometimes if he grabs something by accident he hangs on). Is this normal for a 15 week old?