There is an article titled "How to Deal When You’re Caught Masturbating: Six decent excuses to have at the ready" in Yearbook Three of Tavi Gevinson's Rookie. Keep in mind that Rookie is an online magazine and book series for teenagers.
We've previously written about Gevinson's Rookie. For example, her edited "Advice for Teens Attracted to Older Men" and “Do It Itself: What We Talk About When We Talk About Masturbation” were filled with advice for nymphets.
Here are the excuses that Rookie advises nymphets to use if they are caught masturbating by their mothers:
Pretend that you were scratching a bug bite, that you were having a weird dream, that you were wondering what it would feel like to be electrocuted, that you were practicing "jazz hands", that you were having a "muscle spasm", or a nymphet could just "own it" and give no excuse at all.