Mae Clarke, who played Elizabeth in Whale’s Frankenstein (1931), was terrified of Boris Karloff’s monster makeup—green and even more ghastly in real life. In fact, the intense actress worried that she’d break down and wouldn’t be able to play the scene where the monster attacks her on her wedding day.
Clarke confided in Karloff, and he told her that she should look at his little finger. When he playfully wiggled the offscreen digit, she would remember that it was only him and not be too scared. And the scene went just fine.