The buttons on Balloon Boy's "shirt" are black when he's visible in the cameras, but are white when he's in the office.
When Mangle is in Kids Cove, a loose eyeball can be seen on the floor, which vanishes when Mangle is not present.
The bow on Bonnie's Custom Night icon clips through his jaw.
Phone Guy indicates that the animatronics use facial recognition systems. This technology was not available to the general public in 1987. These systems began to be used by the army and police forces until ten years later.
Phone guy welcomes you the player to your "new summer job" however the game is set in November.
Phone Guy calls Mangle a "he" on Night 3, despite Mangle being included in the "Ladies Night" preset of Custom Night.