Chipmunks have got a brain pan of a marshmellow. I'm surprized he's got a head at all . If you draw a line back from a rabbits eye and down from his ear, theres a nice soft spot or kill zone. I like to study game skulls, bone thickness,lobes etc.. Works for me when taking head shots. Even keep a few on hand for targets , call me weird it but it makes a difference when I know what I'm going through.