Laughed out loud when...
Alistair Sims cuts himself to smear blood on the dolls dress. His facial expression had me rolling for at least a minute. It was made even funnier because he was smiling in a nonchalant sort of way before he cut himself. The sudden change in his expression as he cuts himself is, to me, a moment of great acting.
Overall, I enjoyed the movie and it exceeded my expectations since I had been putting this one off for years knowing that it was not considered one of Hitchcock's better efforts.