The Misfit Sprang up as if a Snake Had Bitten Him

My favorite simile of A Good Man is Hard to Find, was the very last simile:

She reached out and touched him on the shoulder. The Misfit sprang up as if a snake had bitten him and shot her three times through the chest.

When I originally read this, I was confused. I thought the Misfit had been bitten three times in the chest. O'Connor craftily placed a key plot element so close to a simile, that the readers who weren't attentive were completely blindsided. They were just as blindsided as if a snake came up and bit them. It's also fitting for the author to compare the grandmother to a snake since much of the class saw her as a slimy, low-level vermin. The Misfit even overreacted like one would to a snake by shooting her not once, not twice, but THREE times. If O'Connor really wanted to be poetic, she could've depicted the Misfit cutting off the grandmother's head to make sure she was dead.