Chimpanzees laugh differently if they're being tickled than if they're playing with each other, and we might be seeing something like that here, involuntary laughter, tickling laughter, being different from social laughter.
チンパンジーの笑いは くすぐられた時と お互いに遊んでいる時とでは 違うんです これも先程のような 違いかもしれません くすぐられた時に意図せず出る笑いは 社会的な笑いとは違います