In the Steel Mill, looking on the floor in Joker's Office next to Harley's old outfit, it's possible to find a positive pregnancy test. Spoiler:This is an allusion to Harley's pregnancy in the "Harley's Revenge" DLC.

In said DLC, however, Spoiler:, this would become nothing more than a red herring, as when the player re-enters the late Joker's office, Batman finds a baby's crib containing the puppet Scarface painted to look like Joker. Surrounding the crib are a number of used pregnancy test strips, all showing a negative result. Inside the crib is another box the tests came in, with the box warning that the tests can sometimes result in false positives.
Contributed by DrakeVagabond
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