On Thursday, a picture of a cat walking on a set of stairs started to go viral. The original post asked readers if the cat was walking up or down the stairs.
4月9日，一張貓咪走樓梯的燒腦神圖掀起討論熱潮。發布這張照片的原帖問道：這只貓到底是上樓還是下樓？

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.
隨后，這個帖子被瘋狂轉載，這只貓到底是上樓還是下樓，網上沒人能取得一致意見。兩大陣營紛紛引用建筑學和生物學知識，不斷為他們的結論尋找依據。

But it's obvious that the cat is going down the stairs.
但顯而易見，這只貓是在下樓。

First, look at the architecture of the stairwell. The nose of the stair treads is overhanging the riser, which has a pebbled texture.
先來看看樓梯的建造結構。樓梯梯面的收邊條伸出了鵝卵石材質的梯級豎板。

This is what the textured rise and stair nose might look like in real life:
下圖或許可以還原梯級豎板和樓梯收邊條在現實中的模樣：

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:
另外，如果仔細觀察，你甚至還能在伸出梯面的收邊條下方看到淺淺的陰影。只有當這只貓正在下樓，走向看向樓梯上方的觀察者時，陰影才有可能出現。光線從上一級平臺照射下來，在梯級豎板上投射下梯面的陰影。

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.
社交新聞站點Reddit上的一名用戶認為，我們看到的不是收邊條，而是梯面上的防滑條，是為防止人們滑倒而設計。但這就意味著這些防滑條必須具有一定高度（從陰影來看），如此一來，這個樓梯就會變得極其危險——人（和貓）都會常常被絆倒。

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."
商業新聞網站Business Insider用戶fred-sof則評論道："側邊墻上用磚塊或石塊砌成的水泥塊一般位于樓梯平臺內部或上方，就是側邊墻上那些淺灰色磚塊形狀的東西。"

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:
他的意思是，磚塊或石塊通常會位于梯面上方，用來搭建樓梯側面的墻體。下圖就是現實生活中的樣子：

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.
最后，Reddit上的眾多評論堅持認為，這張照片完全就是一只貓下樓時的樣子——尾巴上翹保持平衡，眼睛注視地面，一步一步走下樓梯。

"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."
"我家的貓上樓的時候基本是跳上去的。"Reddit用戶ktphoenix說，"前爪先著地，然后才是后爪。只有在他下樓的時候才雙爪交替走下來。從這一點，以及樓梯突起部分來看，我很肯定這只貓是在下樓。"

Obviously people can see it both ways, but you're only correct if you say the cat is going downstairs.
當然，每件事都會引起不同的觀點。但只有當你說這只貓正在下樓時，你才是對的。

Vocabulary:

stair tread: 樓梯踏板

texture: 質地；紋理

stair nose: 梯面的收邊條

stair grip: 梯面上的防滑條

（譯者：清歡君 編輯：陳丹妮）