Corrected entry: After Batman hits Joker with a net and pins him to the ground, he gets out of his jet and hops down. There is a chicken leg next to the jet from Joker's previous attack. But when Batman is getting back in while Superman and Robin are talking, the chicken leg has disappeared. (00:13:45)
Correction: The shot isn't continuous in any way. By the time Superman comes, the police have already arrived, taken Joker, and left. Plenty of time to pick up objects that belonged to the Joker.
Bishop73