oh, sorry, looks like my bad english is in full effect, its just round balls, small round balls that make people loose their grip on the ground and fall (marbels), and the sound bomb explodes on impact creating a sound close to that of a bottle exploding due to pressure, or something like that.

(1:47) 
[youtube]X4Lb_Xz5o3s[/youtube] 
PS: dont do this at home kids