The Princess Bride
The ROUSes were played by midgets. The actor who played the giant rat that Westley battles was actually pulled over for speeding and arrested (why he was arrested for speeding was never clarified) the day the scene was scheduled to be shot, so the scene was delayed until Rob Reiner and co. could go and bail him out of jail.
Indian Jones – The Last Crusade (1989)
The thousands of rats used in The Last Crusade was insured. The insurer wanted to know the minimum number of rats the scene could be shot with, and used the answer to write a policy with a “1,000 rat deductible.” The cast was padded with another thousand mechanical rats. Their voices were enhanced with the sound affects of … chicken voices.