Mistaken for a grooming ritual
A grooming ritual was a cultural practice among some people and animal groups in which an individual of a species groomed another.
In 1947, Professor Jeff speculated that Rom and Nog were engaging in a grooming ritual. Garland found the action "sweet", and additionally suggested (correctly, as it happened) that they were father and son. In reality, Rom was checking Nog's malfunctioning universal translator, which was located in his ear. (DS9: "Little Green Men")