Todd Phillips’ Joker, an ode to Gotham’s clownish alpha bad guy and the pessimistic, morally ambivalent cinema of the 1970s, isn’t meant to be connected to any canonical Batman continuity. But, that does not mean Phillips didn’t have a little fun with Easter eggs planted throughout his film.

He revealed one such Easter egg in an Instagram post that collected color and black and white behind-the-scenes stills. They show Joaquin Phoenix in various stages of Joker make-up; Phillips on set and seated next to Robert De Niro at Murray Franklin’s desk; and a look inside Arthur Fleck’s belongings.

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The third to last photo is of Arthur’s notebook. It’s open to a page that contains a sly reference to another, more seductive Batman foe, Catwoman. On the page, the word “step” is written repeatedly around a small collage of clip art. A combination of magazine cut-outs and sketches, the collage has one pic which gives the impression a scantily dressed model is riding on a cat.

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The other is of a cartoon cat swinging a ball of string with the bottom half of a woman wearing lingerie pasted on top of it. This could be a tongue-in-cheek allusion to Catwoman’s famous whip and her outfits which, at times, leave little to the imagination. Halle Berry’s costume in her ill-fated solo effort is a good example.

Joker is filled with little references for sharp-eyed viewers to pick up on though you probably won’t catch them during your first watch. Not only are there clippings that evoke Catwoman, but a plot point mentioned a few times concerning “super rats” infesting Gotham traces back to Ratcatcher according to We Got This Covered.

Then there’s one that can be seen when Arthur pays a visit to Arkham. In the elevator with the unstable patient, there are question marks scratched onto the walls. Fans who noticed immediately thought of The Riddler.

Whether Edward Nygma is committed to the facility or he has a tormented antecedent like some theorize Fleck is for the real Clown Prince of Crime is anybody’s guess.

Related: Here’s What Zoe Kravitz Could Look Like as Catwoman in the Upcoming Batman Film

Both Catwoman and Riddler will be in Matt Reeves’ The Batman, played respectively by Zoe Kravitz and Paul Dano. Joker might turn up later if Reeves’ highly anticipated film indeed becomes another trilogy for the Dark Knight. However, we’re betting it won’t be Joaquin Phoenix as The Batman isn’t supposed to exist in the same timeline as Joker.

As for Ratcatcher, a version played by newcomer Daniela Melchior joins The Suicide Squad in James Gunn’s soft reboot that comes out two months after The Batman.

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What do you make of this tease of Catwoman? Leave us a comment.