The rawhide bone is a bit messy, so we'll use this doggy treat as a model for an IgG antibody molecule, with its two identical antigen-binding sites, one at each end. (Note one limitation of this model, namely that it does not show the "Fc" region which gives antibodies their typical "Y"-shaped character. But since the Fc region doesn't affect antigen-binding, this is OK for our purposes.)