Commuters in Berlin, Germany, didn't realize they had boarded the pony express last week until a woman brought her Shetland pony onto the train.
A YouTube video apparently taken on Berlin's S-Bahn subway shows passengers snapping pictures and taking video of the pony standing quietly on the train.
The woman holding the leash doesn't seem concerned about confining a live animal in a small underground space.
Passengers laughed and expressed shock at having the hum drum of their day interrupted by a horse, according to the Daily Mail.
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Authorities are not amused.
"This clearly violates our conditions of carriage," a spokesman for the S-Bahn reportedly told the Daily Mail.
"A horse can be dangerous. What if it escapes?"
The S-Bahn said it was reporting the incident to police. The video has more than 300,000 views on YouTube.