A spokeswoman for the Royal Botanic Gardens in Kew, London, is flummoxed. "A seed might be able to germinate in the damp, dark conditions of a lung, but it's still bizarre," she says.

The gruesome photo released with the story claims to show the spruce jutting from a clump of Sidorkin's lung tissue. The plant looks firm and healthy, with bright green needles. It's as if it had been grown in the best soil with plenty of sunlight. It lacks roots in the way fresh clippings do.

Lungs are good at getting rid of unexpected visitors. They are lined with mucus that traps everything from mould spores to flies. This is pushed out of the lungs by tiny hairs called cilia. You end up coughing it out, or swallowing it.