Why did the chicken cross the rails?

Who knows — but one doing just that held up a downtown 1 subway train on April 20, a straphanger told The Post.

“The train conductor matter-of-factly announced that we were delayed because a chicken was crossing the tracks with a chick behind it,” said the commuter, who declined to be named.

“I looked at the woman across from me … wondering if we were going insane, or actually heard what we just heard. That then turned to laughter. There were several people on the train who had no reaction — I guess [New Yorkers] are numb to the crazy things we hear and see every day,” the rider said.

The fowl-up didn’t last long — just about five minutes, the rider recalled, as the train approached Rector Street in Lower Manhattan.

Critter-caused delays occasionally muck up the city’s sprawling transit system.

In 2018, a wayward cormorant blocked a 7 train in Queens. The bird was netted by NYPD Emergency Services Unit officers, who transferred it to a cardboard box and drove it to Animal Care and Control.

A runaway dog named Dakota created a rough ride for passengers in February 2018 when she escaped from a dog park mid afternoon and was seen running through the tunnel from the York Street station toward Jay Street/Metrotech in Brooklyn. Three lines had delays as the MTA shut down service to rescue Dakota, which took more than an hour.

In August 2018, two goats roamed N train tracks in Borough Park that were, fortunately, shut down for repair.

Once the naughty kids were finally caught, comedian Jon Stewart stepped in to transfer them to an upstate animal sanctuary.

Raccoons crawling through subway tunnels cause five or 10 delays per year. An appearance by one of the masked critters led a straphanger in 2019 to tweet an appeal to subway officials saying, “yo there’s a whole ass raccoon at the platform Brooklyn bound at Nevins St. can you help him?”

Humans also cause delays. In 2019, J trains to Jamaica were snarled after the train crew needed an emergency bathroom break.