Also, we replaced “grab
and tickle” by “flip over”, where the experimenter picks the animal
and flips it on its back. This component is also effective to elicit 50-kHz
calls and has face validity to rat rough-and-tumble play, namely
pinning. Identical to tickle test A, each component lasted 30 s and was
applied between 2 and 4 times on every test day. Also, six “breaks”
were performed again at irregular time points