"The study aimed to assess the effects of unpredictable chronic mild stress (UCMS) during prepuberty and adolescence and the propolis supplementation on cognitive functions in adult male rats." ...

This response suggests that the rats enjoy both the journey and the rewarding destination. Research has also shown that desirable low-stress rat environments retune their brains' reward circuits ...

Later, in 2016, researchers found that, also like us, rats need to be in the right mood to enjoy being tickled. Stressed rats won’t laugh when they are tickled; only happy ones will.