Wildlife Spotting

Without knowing the species of oak, the gall wasp species I'm suggesting can only be that: a "suggestion."

I found similiar galls recently, http://www.projectnoah.org/spottings/14034048, I would hate to cut them open, would that not kill the insect?

The leaf looks like bur oak (Quercus macrocarpa)

Your gall is probably formed by the larva (grub) of this tiny wasp. We would love to see inside if you find the courage to cut it. This is the kind of wasp likely to eventually emerge. http://joycegross.com/sample.php?i=17 http://www.whatsthatbug.com/2007/08/10/crystaline-gall-wasp/

Galls are pretty typical on oak leaves at this time of year. If you cut it open, you'll find a small bug.

This is a Plant gall