One of the biggest mysteries in the history of the Five Nights at Freddy's series is the Bite of '87, but the culprit just might be Toy Chica. Scott Cawthon has been tight-lipped about the incident ever since the series first started, and fans have been speculating about it for just as long. The animatronic that actually did it might never be known, but some are stronger candidates than others.
The Bite of '87 is only mentioned once, in a phone call by the "Phone Guy" in the original Five Nights at Freddy's game. He states that this incident is why the animatronics no longer walk freely during the day, and that the victim survived the incident, albeit with severe damage and/or destruction of their frontal lobe. Details about it have come few and far between, and it's remained a mystery for the entirety of the FNAF series' existence. FNAF theories like Security Breach's Monty killing Bonnie are in no shortage, and every fan has their own opinion on who committed the Bite. A similar incident, the Bite of '83, was shown in FNAF 4, but there have been no references to '87 outside of the first game.
Toy Chica is one possibility for the culprit of the Bite of '87. Due to the shape of her mouth and the fact that it's removable, the incident may have already occurred before FNAF 2 took place. Other animatronics are less likely, the Withereds especially so, so there's a small pool of candidates. The series' in-game history is long and twisting, and since it's never explicitly stated that the Bite occurred before or after FNAF 2, it's entirely possible that it had already happened by the time Jeremy Fitzgerald started working at Freddy Fazbear's. FNAF is a popular horror franchise for reasons that include its complicated lore.
Toy Chica Could Have Committed The Bite Of '87
One of the main arguments for Toy Chica being responsible for the Bite of '87 is the shape of its mouth and beak. It's famous for removing its beak and eyes at the start of each night, but that raises the question of why it was designed to be removed. None of the other animatronics have this feature, after all. If one takes a close look at the shape of its beak, they will see that it would appear to be rather rigid and immobile, and it may not be able to open its mouth very wide. It's almost as if the beak is designed to act as a muzzle, to prevent Toy Chica from biting again. The reason that it can be removed at all could be because the inner mechanisms such as the voice box still need to be accessed.
When decommissioning Chica in FNAF: Security Breach, its mouth is destroyed, showing that the voice box is at some point located in this area. The fact that Classic Chica's mouth has a set upper beak, and that the lower beak is made with a rotating cylinder that seemingly wouldn't be able to generate much force, and that every Chica made afterward looks like they're similarly designed to have little-to-no movement and clamping power in their beak, corroborates this idea. Withered Chica's jaw might be broken, but its mouth is as big as, and shares the same design as, the rest of the animatronics', which is further evidence.
Another piece of evidence is that Toy Chica is a "party" animatronic. Its bib says "Let's Party", and due to this iteration's redesign to apparently be more fun and playful, it stands to reason that it was brought out for birthday parties and special celebrations. Chica's pizza obsession in FNAF: Security Breach, the classic version's bib stating "Let's Eat", and Chica's general reputation surrounding pizza and eating all indicate that it's frequently chewing and biting, perhaps eating a slice of pizza so as to not upset a child offering it some, which may in fact be what caused the Bite. Such events have a lot of people to act as potential victims, and a lot of chaos that could overwork its AI, causing it to malfunction and clamp its mouth shut at the wrong time. In the Night Six phone call, Phone Guy states that there will be a birthday party the next day, and warns Jeremy to keep the animatronics from hurting anyone. It's possible that by "animatronics", he means Toy Chica particularly, and the warning could be born out of a similar previous incident.
What About FNAF's Other Animatronics?
Of course, Toy Chica is only one animatronic out of many, and there are other candidates. Every FNAF game has its own scares and animatronics. There are many in FNAF 2, but only six were in service during the events of the game, and in the time leading up to it. Toy Freddy, Bonnie, Chica, Foxy aka "The Mangle", the Puppet, and Balloon Boy are the only ones that feasibly could have done so. The Mangle is a popular candidate in fan theories, but one must remember the Bite of '83. Fredbear's jaws crushed the head of the Crying Child, leading to their death, and the fact that the Bite of '87 victim lived through the incident, seemingly with damage only to their frontal lobe, points to the animatronic that committed the Bite of '87 having a smaller mouth, which the Toy Animatronics have. Aside, that is, from Mangle, whose mouth is comparable to Foxy's in size.
The scariest characters in FNAF induce nightmares, but some are more likely to commit the Bite of '87 than others. The Bite of '83 also means that the proprietors of FNAF 2's Freddy Fazbear's location could have been wary of letting Toy Freddy get close enough to anyone to bite them, which makes him less likely than others. Balloon Boy is far too short to do so, and it and the Puppet both serve roles that make for very brief interactions with customers. Bonnie is a less-popular animatronic than most, often shunted to the sidelines, and although it's another feasible candidate, there's less evidence in its favor than there is in Toy Chica's.
Is It Possible That The Bite Of '87 Occurred Before FNAF 2?
Of course, everything hinges on the Bite of '87 taking place before FNAF 2, which isn't guaranteed. There is some evidence that it occurs after, but nothing is concrete. FNAF has lots of locked doors hiding hints in its lore (metaphorically speaking), and many things are still unknown. The animatronics are not allowed to walk around during the day in the original FNAF, which the Phone Guy explicitly states is due to the Bite of '87. This decision could have been made after the closing of the second Freddy Fazbear's location, however, especially considering the franchise's famous disregard for safety precautions, as well as the fact that serial killer William Afton was in charge of security at the time. The Night Six phone call references him being discovered killing children some time during the events of the game, so the company could have rewritten its policies after this incident.
It's also strange that the second Freddy Fazbear's would stay open after another biting incident when Fredbear's Family Diner closed after '83. The '87 victim did survive, however, when the Crying Child didn't. Explaining all of FNAF's endings is enough to bring on a headache, but that much is known. It's possible that the company was tangled in litigation at the time, which would have been resolved when Afton was discovered killing more children in FNAF 2. The Bite of '83 was also due to human error, whereas there's no evidence that the Bite of '87 was anything but an accident. Freddy Fazbear's lack of safety protocols means that altering Toy Chica's head was likely the bare minimum that it could do to prevent further incidents and show a semblance of precaution while lawsuits were going on, which fits the company well given its history.
The restaurant may have still been operational and receiving customers because FNAF 2 takes place late in the year, and if the Bite of '87 was early in the year, there would have been plenty of time for the scandal to die down. FNAF 2 isn't the series' lowest rated game, in fact, it's quite the opposite, and the fact that it's the one that followed the original means that Scott Cawthon may have had a culprit for the Bite of '87 in mind when he made it, if he didn't already. In-game, it's stated that the company also spent "a small fortune" on the animatronics, which means that it could have had deeper pockets than Fredbear's Diner, and explain why it kept Toy Chica and the rest operational post-Bite. The entire theory may be a long shot, but the fact that it's so convoluted means that it fits right in with existing Five Nights at Freddy's lore.