Here's something I texted to my friend a few weeks ago:
'Now the bite of 87 is when a security guard (supposedly Jeremy Fitzgerald the guard for the first five nights in fnaf 2, is 'bitten' in the head by a fnaf 2 animatronic, theorized to be either mangle, Withered foxy, or toy chica. The proof for toy chica bitting the security guard is in ucn with one voice lines after you get killed by her which has her say: "Where's my beak? Loged in your forehead of course."
Now, the frontal lobe is located in the fore head area so it would make sense of who caused the bite of 87'