For a change from all the experiments that stress rats and mice in various ways, here's somebody who studies what makes rats happy--and finds that male and female rats like to be tickled in different ways.
Summary: https://www.sciencenews.org/article/rats-tickling-preference-happiness
Original paper: https://royalsocietypublishing.org/rsbl/article/22/4/20260075/481317/Sex-differences-in-the-enjoyment-of-enrichment










