I rounded the white oak tree, and there they were at eye level. Bullet exit holes.
The pea sized galls fed and sheltered the larvae of a tiny wasp ( Disholcaspis quercusglobulus ?). Once the larvae were mature they exited to lay eggs on another twig and other white oaks were given instructions to grow Round Bullet Galls. Note the scar on the twig where a gall detached.
This cut-away view shows the home/pantry the wasp induced the oak to grow for it.We humans think we are so intelligent. I wonder why we couldn't practice a bit of biomimicry and inject an oak tree with the some concoction. Then the tree would grow us a house and while we are comfortably sheltered, feed us. Yes, galls are fascinating, and exit holes leave me wondering.