To all the usual reasons that the Red Line gets delayed — aging vehicles, signal failures, switching problems — add a new one: a missing snake.

The MBTA held up a Red Line train at JFK/UMass station and again at the Braintree terminus after a female passenger reported losing a snake on the subway just before noon yesterday, T spokesman Joe Pesaturo said.

The woman became concerned that she could not find Penelope, her pet snake, as the train surfaced between Andrew and JFK/UMass stations. At the stop, the MBTA held the train for about four minutes as T employees helped search the car in which the woman was riding, but Penelope was nowhere to be found.

Not wanting to cause further delay, the T ran the train as scheduled for five stops to Braintree, where the train, by then empty, was held so that Red Line personnel and the MBTA Transit Police could examine each of the six cars, accompanied by the woman.

The search was called off a little after 12:30 p.m., and the train was returned to service. Pesaturo did not know what species of snake was reported missing, but said officials were confident that the train was safe and reptile-free.

Patrick Garvin, a graphic artist for the Globe, was riding the Red Line when the woman boarded downtown. Though the train was about three-quarters full, he said, she cut a memorable figure, dressed business-casual, but with sections of her hair dyed purple, as she dashed for an empty bank of seats.

Shortly thereafter, he said, she began rooting through her purse, the way one might dig for a lost cellphone, before bending down to search under the seats. Increasingly frantic, she appealed for help in finding a snake.

“She was pretty distraught,’’ Garvin said. “She was like, ‘It was just around my neck a second ago. God, my husband’s going to kill me!’ ’’

Some passengers knelt down to help. Others backed away, looking horrified. When the train reached JFK/UMass, some raced for the exits.

“I could see why people were freaked out,’’ said Garvin, who was briefly part of the search party.

The T does not expressly prohibit snakes. Guide dogs and other service animals are allowed at all hours, while nonservice pets are allowed only during off-peak hours. Dogs should be well behaved and properly leashed, while small domestic animals must be carried in lap-size containers and kept out of the way of exits, according to T policy.

In August, T officials briefly detained a Green Line trolley on the D Line after passengers reported that they felt uncomfortable because of a rider carrying a snake around his neck.

By the time police responded to the Brookline Village Station, the man and the snake had already exited.

Eric Moskowitz can be reached at emoskowitz@globe.com.

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