Bava Kamma 18 - Breaking a Broken Utensil

If one threw a utensil from the top of a roof, and someone came along and shattered this utensil in midair with a stick, is the one wielding the stick liable, or has he merely broken a broken utensil? Is the utensil considered broken form the start of the process?

Can we rely on another ruling: if chickens were pecking at the rope of a bucket, and it snapped, and the bucket broke, the owner of the chicken is responsible for damages. Is it because the bucket is broken from the beginning of the fall and thus the chickens are directly responsible? No! Damages for the rope.