A team of international student volunteers posing for a portrait at the end of their sojourn in Costa Rica were joined by a surprise intruder: a sloth, who slow-bombed the picture at the last second.

The furry little leaf-eater, usually  linked to inactivity and lazing about in trees, dropped down as photographer Manuel Ramirez, 44, was about to push the button and shoot.

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A squirrel jumps up and is caught in a time-delayed photo of Melissa Brandts and her husband in Banff National Park three years ago. (Melissa Brandts)

"As I looked through the camera lens, I could see something creeping in to the frame," Britain's Telegraph news website quoted him as saying. "When I realized it was a baby sloth, I clicked the button as fast as I could — not that he was going anywhere fast."

It harkened back to the moment three years ago in Alberta's Banff National Park when a squirrel jumped up and was caught in a time-delayed photo of Melissa Brandts and her husband.

The sloth was on its way Friday to achieving the same viral status as the squirrel.