???"Whip crack!" from song of goblins, when they seized Bilbo and the dwarves.
"Swish, smack! Whip crack!
Batter and beat! Yammer and bleat!
Work, work! Nor dare to shirk,
While Goblins quaff, and Goblins laugh,
..."

Question

???"Whip crack!" from song of goblins, when they seized Bilbo and the dwarves.
"Swish, smack! Whip crack!
Batter and beat! Yammer and bleat!
Work, work! Nor dare to shirk,
While Goblins quaff, and Goblins laugh, 
..."

Answer

I think this refers to the sound a whip makes when used.  We say it makes a cracking sound.