The giant anthills are real and were an accidental discovery while filming Hermit Bob in the woods. Jim liked them so much he added the scene and dialogue spontaneously.
According to Jim Jarmusch, Iggy Pop asked him prior to shooting what the backstory for his zombie character was and Jarmusch explained he and his girlfriend were killed on his motorcycle in 1973 after leaving a Blue Öyster Cult concert. Iggy Pop actually performed with Blue Öyster Cult and Kiss in 1973.
When the three cops are driving down the road toward the cemetery, Adam Driver's character leans out the window with a machete to cut off the head of one particular zombie. This zombie is dressed in the same clothes and with the same hair as Bill Murray's character in the 2009 zom-com Zombieland.
The movie is filled with references to George A. Romero's Night of the Living Dead (1968), including an appearance of the infamous naked zombie played by the original actress. Also, the three hipster teens are mistakenly believed to come from Pittsburgh, the city Romero studied and started his director career in.