In last week's episode of The Walking Dead, one of the most memorable scenes was when Rick (Andrew Lincoln) was pushed off of a massive trash heap and into an area where he was forced to fight a spiked zombie, in an effort to prove himself to this mystery group's new leader, Jadis (Pollyanna McIntosh). Just before that, though, there was a scene that showed Rick standing atop this heap, which was meant to show just how expansive this junkyard world really was, but it also revealed something else. One eagle-eyed viewer noticed something mysterious flying past in the background, which could be anything from a simple airplane, to an alien UFO.

Twitter user AngelLuis was the first to point out this phenomenon, capturing a brief video on Sunday night, presumably from a DVR recording, and tweeting it to the after show Talking Dead, asking, "What's behind Rick? UFO? Plane? Bad editing?" There is one object that "stands out" the most, since it flies directly behind Rick's head, but in this close-up video from Angel Luis, there are three more objects that are "flying" or moving along the tree line, which could be anything from birds to cars, but they can't exactly be made out. While both birds or cars are acceptable answers for the three lower objects, the black speck that flies past the back of rick's head is too big and is going way too fast to be a bird.

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While many fans may assume that there was simply a plane travelling in the background during this shot, and the show's producers decided to keep it in, that may not be the case either. While discussing his big zombie fight in the episode, Andrew Lincoln revealed in a recent interview that the crew did make quite a large practical set for this junkyard, but he also stated that they used a blue screen to extended the set digitally. Here's what Andrew Lincoln had to say in his recent interview.

"It was wild. We were still shooting other episodes while it went up and it happened within something like three days, they delivered this junkyard. And they kept building and building and building this crazy Mad Max landscape. And then we did the CGI with the blue screen for several scenes, and I haven't seen it, but you get this maze that just goes into the distance."

The scene with Rick standing atop the trash heap with Jadis would clearly be one of the scenes they use the blue screen, since we see in the episode that this junkyard is much bigger than previously imagined. If there was a blue screen background during this shot, that could only mean that these mysterious flying objects were added on purpose in post production, or it could be some sort of glitch, but that seems unlikely. It's worth noting that Robert Kirkman, who created the comic books the show is based on, has joked in the past that aliens are what caused the zombie apocalypse, since he has made it quite clear that he will never reveal what actually caused the dead to rise in this world. This "UFO" could be just a not-so-subtle nod to that joke as well. It isn't known when we'll see this junkyard set again, since next week's episode, Hostiles and Calamaties, seems to largely take place at The Saviors' compound known as The Sanctuary. Take a look at this video below to see the strange "UFOs" that fly past Rick on last week's The Walking Dead.