We once has a new litter of kittens at Christmas and they were great fun chasing each other up and down the tree, hiding in the presents, falling asleep in front of the fire.
It was idyllic under we started to notice an increasingly disgusting smell which I eventually tracked down to the kitten shyte in the soil of the Christmas tree. It had roots, which we watered, so the tree was drawing it up and sending the stench out of the needles.
I had to bin the lot and the kittens didn't get their mittens.