plural

According to a news report, a certain private school in Victoria, Australia,
recently was faced with a unique problem.

A number of 12 year old girls were beginning to use lipstick and would put
it on in the bathroom. That was fine, but after they put on their lipstick
they would press their lips to the mirror leaving dozens of little lip
prints. Every night, the
maintenance man would remove them and the next day, the girls would put them
back. Finally, the principal decided that something had to be done.

She called all the girls to the bathroom and met them there with the
maintenance man. She explained that all these lip prints were causing a
major problem for the custodian who had to clean the mirrors every night.

To demonstrate how difficult it had been to clean the mirrors, she asked the
maintenance man to show the girls how much effort was required. He took out
a long-handled squeegee, dipped it in the toilet, and cleaned the mirror
with it.

Since then, there have been no lip prints on the mirror.