There are two notable paper clips on the file Batman gives Joker. When Joker gives back the file, one of those paper clips is missing. Joker of course escapes the insane asylum eventually; and now we know how.
Review of The Batman: Deleted Arkham Scene
The Batman: Deleted Arkham Scene
(2022 Video)
One reason this scene was made/released
6 July 2022
Warning: Spoilers