The beak of the red-headed woodpecker (Melanerpes erythrocephalus) hits the bark of a tree with an impact velocity of 13 mph, subjecting the bird's brain to a deceleration of approximately 10 g when its head snaps back. Other woodpeckers my experience an even higher g-force.
How do you know Verne was talking about shooting normal humans out of a cannon and not liberal pea brains?