CEDICT
to flirt; to make out with; to philander with
Wiktionary
男女間的挑逗行為。
重編國語辭典
藉由語言、文字、神情或肢體語言含情地挑逗、取悅或魅惑他人;常帶有性的意味
維基詞典
Tom flirted with Mary.
Source: Tatoeba
They are not singing, they are flirting with each other.