A man in Russia has amazed doctors after they found a tiny fir tree growing in his lung.
Artyom Sidorkin started getting strong chest pains and he thought something was seriously wrong with him.
Doctors took X-rays and spotted what looked like a cancerous growth in one of his lungs.
So he had a routine operation to get rid of it but it actually turned out to be a tiny fir tree - although it's not clear how it got there!
The 5cm tall fir tree appeared to be growing inside him.
Surgeon Vladimir Kamashev said: "The branch was green, as if it had just been taken from the wood. It's still a mystery how the tree got in there."
Some people think Artyom - who studies plants for a living - breathed in a branch while he was working in the woods.
Others believe he inhaled a seed which then grew into a tree inside his body.
But he doesn't think that's possible: "For plants to be able to grow they need light, water and carbon dioxide. Therefore, plants cannot use human tissue, they cannot process them."
Artyom may be getting an answer soon. Part of his lung - along with the tree - has been kept to be studied further.