A girl is a freshman and has a biology practical in which she has to study dead skin cells under a microscope. As usual the tutor tells her to scratch along the inside of her cheek with her nail or with a spatula a few times in order to get the necessary skin cells. Then she has to place the collected material on a slide, put a piece of plastic on it, and put it under the microscope to examine it. The girl does all this and sees something moving in the sample. She doesn't know what it is, and asks the tutor whether he does.

The tutor looks at her sample through the microscope and says it isn't very important. The girl, however, is determined to know what it is and urges the tutor to tell her. The tutor refuses several times, and by the time he is finally prepared to tell her, the attention of the other students has of course been attracted. Eventually, the tutor says that the moving bits are male sperm cells, whereupon the girl blushes heavily; she had had oral sex with a boy that morning.