smack的意思是“拍击、打，并且声音很响”，smack lips就是用双唇之间互相碰撞并且同时会产生响声的一个嘴部动作。smack one's lips 咂嘴；热心地期盼

【例句】
"I love chocolate cake," said Susan, smacking her lips.
“我喜欢巧克力蛋糕，”苏珊边咂着嘴边说道。

Property developers have been smacking their lips at the thoughts of getting their hands on such prime real estate.
地产开发商们已经迫不及待地想要取得如此优质的地产开发权。