Mark Knopfler, who composed the music to the Princess Bride, only agreed to do so if Rob Reiner could include the baseball cap he wore in the film Spinal Tap. The director placed the cap in the boys bedroom, beside the bed.

When Count Rugen knocks Westley out to put him in the Pit of Despair, Cary Elwes wanted the scene done properly, so he told Chris Guest to hit him for real with the sword butt. Guest did, and accidentally hit him hard enough that production had to be shut down for a day while Elwes was taken to the hospital.

Around the time that Buttercup tells the man in black about Westley, Cary Elwes had an accident with a small four-wheeler and severely injured his foot. Because he didn't want to delay the shoot, Elwes did the scene anyway, and you can see him favoring his right leg the entire time.

In the scene where the R.O.U.S. is snuffling around, it's the director, Rob Reiner, who is making the snuffling noises.