Shortly after the ghost cuts the girl's throat, Dr. Stringer is holding Kristen while the nurse is giving her a shot. When it cuts to a close up of the shot, Dr. Stringer is gone, then reappears after the camera cuts back.
Although Electroconvulsive therapy (ECT), formerly known as electroshock, is still used today in the U.S., it is only used as a last resort, with patient consent (except in the most extreme cases), and with the patient anesthetized, not awake and screaming like a tortured banshee as depicted in the film. Also, the ECT machines used in the U.S. today make the procedure quick and relatively painless (e.g., no noticeable twitching or spasming of the muscles). However, the movie is not set in present time but rather in the 60s, as Dr Stringer revealed during his last session with Iris.
The goof item below may give away important plot points.
Incorrectly regarded as goofs
While Kristen undergoes electroshock therapy, the doctor is holding her down. Her body trembles while the doctor remains unaffected by the shock. However, it's later revealed that Kristen was never real, and that Alice hallucinated most of what happened to Kristen, meaning this may or may not have happened.