Under which rib did Abner smite Asahel?

Under the fifth rib

Abner with the hinder end of the spear smote him under the fifth rib, that the spear came out behind him; and he fell down there, and died in the same place: and it came to pass, that as many as came to the place where Asahel fell down and died stood still. 2 Samuel 2:23