回したり転がしたり。カワウソはなんでこんなに石遊びが大好きなの?その理由を科学で検証(英研究) (4/4ページ)
The drivers and functions of rock juggling in otters | Royal Society Open Science
https://royalsocietypublishing.org/doi/10.1098/rsos.200141
References:Why Do Otters Juggle? | IFLScience/ written by konohazuku / edited by parumo