Continuity mistake: When Doleman is roleplaying with McKern, initially the chains are properly attached to his handcuffs. But when they start talking about spikes, he's holding the chains in his hands.
In the chapel, you can see the heads of those who tried to cross Harriet (the mad matron) preserved in formaldehyde. How did she get hold of so much of it? Wouldn't her husband or the headmaster be suspicious?