Behold the horseshoe crab. An ancient creature, he is not really a crab at all but is closely related to ticks, spiders and scorpions. Horseshoe crabs swim upside down and have a dozen legs and molt 16 times. Their tails are used as rudders, for navigation, and to flip themselves over when they are upended by strong currents or thoughtless humans.
So it is with little G. He's four months old now and he's decided to learn how to roll. The child will smile and squeal and giggle and lunge and...almost roll over. He can achieve face-down position but he gets stuck on his own arm. He cannot yet pull it out from under himself. So there he lies, happy as a horseshoe crab, until he uses his arm as a lever to upright himself.
And try, try again.