On Thursday, a picture of a cat walking on a set of stairs started to go viral. The original 9Gag post asked readers if the cat was walking up or down the stairs. 

The story has since exploded and no one online can agree if the cat is running up or down. Commenters in both camps keep citing architectural and biological reasons for their conclusion.

It’s getting ugly.

@businessinsider Well thank you Business Insider but WE can figure it out.. The cat is most certainly going UP the stairs. We're sure of it.

— Qwyvr (@Qwyvr) April 9, 2015

But it’s obvious that the cat is going down the stairs.

First, look at the architecture of the stairwell. The nose of the stair treads is overhanging the riser, which has a pebbled texture. 

This is what the textured rise and stair nose might look like in real life:

Plus, if you look closely, there’s even a slight shadow under the overhanging nose of the stair treads. These shadows would only be visible if the cat was going down the stairs towards the viewer who is looking upstairs. The light coming from the upstairs landing is causing the shadow of the tread to fall on the riser:

One Redditor suggested that what we're seeing are stair grips — not a stair nose — to keep people from slipping. But that would mean the stair grip would be ever-so-slightly raised (we know this because of the shadows), which would be extremely dangerous — people (and cats) would be tripping all the time.

Then there’s this comment from Business Insider reader fred-sof: “The cemented in brick/stone in the side walls are placed in and on top of the step landings, they are the light grey brick shape items in the side walls.”

What he means is that bricks or stones are typically placed on top of step treads to build up the wall surrounding the stairs. Here’s what that looks like in real life:Finally, numerous commenters on Reddit insist that this is simply what a cat looks like when it’s going down the stairs — tail up for balance, eyes focused on the ground, and taking the stairs step by step.

“When my cat goes up stairs, he kind of hops up them,” said Redditor ktphoenix. “Front paws first, then back ones, and on up. It's only when he's coming back down that he actually walks one paw at a time. That and the position of the ledge makes me pretty sure it's down.” 

Obviously people can see it both ways, but you're only correct if you say the cat is going downstairs.

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SEE ALSO: No one on the internet can figure out whether this cat is going up or down these stairs