There's a LOT of in-jokes in the Duncan and Mallory pages.  On the first page, at the top, you can see Anubis waving to Abraham (who's off herding sheep) as Bast stands at a bus stop, waiting to go to work.  In the parallel universe, the little girl is reading a guide to mythological animals -- but as you can see in a closeup of the other panel, the unicorn girl is reading "Tales from the Vulgar Human."

This is a direct reference to Bob Asprin and Lynn Abbey's second Thieves' World anthology, "Tales from the Vulgar Unicorn."