It seems that the makeup artists on "Star Trek," without asking beforehand, shaved off Craig's eyebrows before applying her makeup. Craig was merely laying still in the makeup chair, so it seems the makeup artists could have sandblasted her face and she wouldn't have noticed. Craig had never shaved her eyebrows before, so she didn't know if they grew back. She was so incensed that even briefly considered legal action:
"I adored Leonard Nimoy, he just had the most droll sense of humor. The first time I went into makeup I had my eyes closed, and when I got home I realized they had shaved my eyebrows. They could just as easily cover them with mortician's wax and I was furious. I said, 'If my eyebrows don't grow back, I swear to God I will sue them.'"
Mortician's wax — indeed, a substance used by morticians — was a common substance in makeup kits and could be used to coat an actor's eyebrows before applying makeup. Morticians use the wax to weigh down a corpse's eyelids for open-casket funerals so that its eyes don't open. Boris Karloff famously used mortician's wax to partially weigh down his eyelids to play Frankenstein's monster.
Craig was comforted about her eyebrows by a jocular Nimoy:
"Leonard said, 'Yvonne, I couldn't help but overhear what you were saying and I just wanted to say when I started the show I went to a dermatologist and he assured me that anyone who can grow a beard can grow their eyebrows back.' And with that he turned and left. So I'm standing there saying, 'Grow a beard?' He was so funny. He has a great sense of humor."