7. Zatanna Skaeps Sdrawkcab
One of the more blink-and-you'll-miss-it references in the pilot of Constantine is, debatably, not necessarily an Easter egg. The backwards writing on the chalkboard behind Liv in that one scene could just have been the art director doing some goofy set dressing; or - more likely considering the wealth of other shout-outs to be found throughout the episode - it could be a sly nod to the magical DC character Zatanna and, more specifically, the way she casts spells by saying backwards phrases. Who knew it was so easy? Besides her father, from whom she learnt the whole magic bag, there isn't really anybody else in the DC universe who uses magic in the same way as Zatanna. As seen in the episode, John has a fair more work cut out for him when he goes about making incantations. More importantly, the pair used to have a "thing" for many years - until Constantine was involved in a botched séance where Zatara sacrificed himself to protect his daughter.
