His facial expression morphs to mimic Gaster’s, featuring a wide, "creepy" smile that occasionally switches to a toothless, open-mouthed grin.
A large fracture forms on the right side of his skull, extending down to his eye, and the blood from his mouth vanishes. Undertale Last Breath An Enigmatic Encounter (Phase 3)
Sans’s eyes flicker with static-like fuzz, and his head shakes rapidly, conveying a sense of instability as Gaster takes partial or full control. His facial expression morphs to mimic Gaster’s, featuring