If you've ever laced your fingers together, turned your palms away from you and bent your fingers back, you know what knuckle cracking sounds like.
 crack knuckles crack joints pop knuckles pop joints就是把一手掌推另一手握拳的指頭而發出咯咯的聲音
你剛剛說了甚麼? 不好意思，我放空了一下。 (請填空)
What did you just say? I am sorry. I just lst my train of thought.