The Endo skeleton is made of metal. Also in actual animatronics the jaws are somewhat the most important part for making characters talk. And skulls are fragile so that much pressure can crush some bones.
HOW STRONG IS FREDBEAR'S JAW TO CRUSH A KIDS SKULL, IS IT POWERED BY AIR CYLINDERS OR SERVO MOTORS; FAZBEAR ENTERTAINMENT INCORPERATED REMINDS THE PUBLIC THAT THE TERRIBLE INCIDENT THAT DEFINITELY DIDN'T OCCOUR ON NOVEMBER 14 1983, DID IN FACT NOT HAPPEN. "FREDBEAR" DOES NOT EXIST. "SPRING BONNIE" DOES NOT EXIST. "FREDBEARS FAMILY DINER" DOES NOT EXIST. HAVE A FAZERIFFIC DAY!"