Forget the blue/black (or was it white/gold?) optical illusion. The is so last year. Now we want to know: Is the animal being petted in this Twitter video a fuzzy black bunny, or a sleek raven?
Daniel Quintana, a senior researcher in biological psychiatry at the University of Oslo in Norway, posted the video to Twitter on Sunday. As of Tuesday, the clip had been viewed 1.7 million times on Twitter, retweeted more than 8,000 times, and liked 33,000 times.
"Rabbits love getting stroked on their nose," a cheeky Quintana wrote. And then the controversy erupted. Because... the animal being petted does look quite a bit like a soft, fluffy black bunny rabbit, except perhaps for some unusually sharp looking ears.
Move your attention to the ears, and... hey, are they ears after all? They might be the major giveaway that this is no bunny, but instead a bird, and the "ears" are its open beak.
Quintana told me that's not his original video. He spotted the clip on a tweet sent by photo service Imgur on Saturday and shared it to his own feed. A representative for Imgur didn't immediately respond to queries about the origin of the video.
"The static bird/rabbit illusion is well-known within psychology and philosophy, so when I saw a video, I thought it would be interesting to share it, " Quintana told me in an email.
Quntana himself was never fooled by the feathers-or-fur dilemma.
"I thought it was fairly clear that the video was of a bird... as you can see the translucent nictitating membrane sweep across the eye horizontally (rabbits don't have membranes like this) and the positioning of the 'ears' are a little strange," he said.
But he intentionally captioned the video to send readers falling down a rabbit hole.
"I made the rabbit comment to prime readers into thinking it was actually a rabbit, to give it a fighting chance at least," he said. "When you only see the beak in your peripheral vision, it really seems like they're ears. Without this misleading cue, I thought most people would have seen a bird."
As for the bird itself, Quintana says, "I'm pretty confident this is a white-necked raven, but I'm not a corvid expert so I can't say this with 100 percent certainty." (Corvid is the bird family that includes crows and ravens.)
Social-media users had fun with the confusion. Was it Duck Season, or Rabbit Season? One Twitter user summed it up nicely, writing, "Not sure if rubbing left looking rabbit on the nose or an upward looking bird on the head (ears=beak)."
Many social-media users figured out the solution on their own. "That is not a rabbit, it is indeed a corvid," wrote one, indicating the nictitating membrane Quintana also noted.
Quintana himself is enjoying the public response.
"I'm surprised to see how popular the tweet has been. I only expected that psychological scientists would be interested, but it's gone much further than my community," he told me. "It seems about two-thirds of people are insisting it's a bird, and the remainder are either insisting it's a rabbit or can't decide."
Now that we've got the bird-bunny controversy straightened out, there are plenty of other confusing animals out there to identify.