Rowling shows that after Lupin led Neville to ridicule Snape in ways the Marauders might have done, Snape conflates Neville in his mind with Peter Pettigrew. Even Harry registers that Peter Pettigrew, in his parents’ photos, “resembled Neville Longbottom.”
Evidence as to why Snape seems to relish in singling Neville out to harass him. Like Harry,Neville shares a striking resemblance to yet another one of Snape's abusers.
