the bite of '87. A FNAF legend.

it was june in freddy fazbears pizza, in the year 1987, this was the the time foxy had fans, wasnt out of order, when the other animatronics didn't shun him, and a time when foxy hadnt had pieces of his body fall off. yes it was a long time ago, but what caused this incident? what caused the great infamous bite of '87?