Monorail Cat refers to a photo fad in which cats on railings, banisters or other thin platforms resemble a monorail trains. The photographs are based on an early viral photo of a cat lying on the metal frame of a mirror with its legs tucked inward, causing it to resemble a monorail.
While it is more likely that Monorail Cat was one of the first products of /b/'s Caturday, the earliest known instance of monorail cat was posted on the website Catmas on November 2nd, 2006. The picture (shown below) features a cat resting on over a metal-framed mirror with its legs tucked inward, which makes the cat look like a monorail. The post was captioned, "It's been a while since we've posted a cat picture, but we're back!"
That day, YTMND  user Cataclaw posted a gif of the Monorail Cat set to music. The post received more than 80,000 views as of November 2017. Additionally, on November 2nd, Cataclaw posted gif entitled "Monorail Cat not amused," which featured the cat "derailing" and received more than 18,000 views as of November 2017. More versions appeared on YTMND, including:
One month later, Catmas posted a gif version of Monorail cat in which the cat moves like a train. The gif (shown below) also includes the text "Monorail cat has left the station."
On December 19th, 2006, the website MonorailCat.com was registered.
Two months later, on January 12th, 2007, the picture first appeared on ICanHazACheezburger, where it became a popular LOLcat. Many pictures are submitted to the site having to do with a monorail cat or dog. Now it is one of the most famous lolcats around.
Monorail cat shirts were later printed by CafePress t-shirt (shown below).
Additionally, if you type "monorail cat" into the game Scribblenauts, you will get a ""weird hidden object."
On October 14th, 2017, Twitter  user @madaomax7 posted a picture of Monorail Cat on a wooden banister with the caption "ネコバスじゃなくて、ネコモノレール？" (translation: Not a cat bus, cat monorail?) The post (shown below) received more than 550 retweets and 1,500 likes in three weeks.
Following this tweet, other Twitter users began posting pictures of their cats in similar positions (examples below, left and center, respectively.
Later that month, Twitter user @zboah tweeted the picture next to a picture of a monorail. The post (shown below, right) received more than 30,000 retweets and 36,000 likes in two days.
On October 31st, Twitter published a Moments page about the return of the meme.
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