>>8386
How about children* decorating a Christmas Tree with their own cut off organs, both external (such as eyes, ears, fingers, toes, maybe whole hands and feet, boobs if there are teen or adult characters, penises and testicles of there are male characters) and internal (such as guts, stomach, liver, maybe lungs and heart, uterus and ovaries). Also not sure if tongue and teeth count as external or internal. Or maybe cut out the whole lower jaw. Or maybe even a whole head.
Instead of every character just giving every organ in the list it should be more random and spontaneous as different ideas come to mind to each character. Most damage should probably be non lethal (and I think anything other than lungs, heart and head can come off as non-lethal) so that after decorating the tree they can actually selebrate Christmas. If there is any lethal damage at all, it's probably just one or two characters (depending on how many there are overall) whose choice of organs to put on the tree just so happens to be something lethal. Everything is done in a cheery holiday atmosphere as if it's a totally natural thing to do for Christmas. Just by the rules of the world, as a natural order of things, characters don't feel pain, but, as T-800 said, fell damage. That is they can tell from their senses when, say, a knife cuts through their flesh, but it doesn't bother them like pain. Either they perceive it as totally neutral or a very week version of pain that isn't enough to bother them, especially when they're having such fun. Also, by the same rules of the world, they don't die unless their heart, lungs or brain are taken. Maybe it's something like the Car Fight universe. But explanation is unnecessary.
Then, if there are lethal cases, death is perceived as an equally natural and harmless consequence as to any other removed organ. As a character decides if they want to put their foot or eye or heart on the tree, it doesn't occur to them to consider that it would hurt their walking ability or sight or kill them, as these are all negligible and not worth consideration, but only consider which they think would look better on the tree and add variety to it (like if there are already enough eyes, maybe I should put my heart instead). What for other characters reacting to someone's death, again as they would only see it as natural. Like if someone puts their both eyes on the tree, it's only natural they can't see anymore. Same way if someone puts their heart, it's only natural that they die.

* I'm thinking Elementary school age, but depending on whether you write guro with such young characters, they can also be teens or young adults. Also can be all girls or both girls and boys.

It can be a whole class of children decorating the school's Christmas tree. In which case it's probably just one item per kid.
Or it can be a family decorating their tree at home, in which case it can have characters of various age groups and probably each character puts more than one thing on the tree until they feel it's properly decorated.