The first time I had a partner into BDSM, I learned that the instinct to protect the eye is extremely strong, so strong that even the suggestion of a threat to its safety has a visceral response. She used that instinct to good effect and I’ve used it with others since. Likewise a number of famous movie posters have used it to sell the experience of the film by simply photoshopping an insect near (or on) the conjunctiva in a closeup shot of an eye. It totally works. The mind is fascinating.