adverb taking the 'to' particle
Mimetic adverb describing a light, sharp hitting or slapping sound, often with the palm or a flat object. Used with と.
彼は蚊をペシッと叩いた。
He smacked the mosquito with a whack.
妹が私の背中をペシッと叩いた。
My little sister slapped my back with a light smack.