The staff at a U.K. cat rescue center in Bradford, West Yorkshire, thought they had seen it all until police dropped off two kittens on Monday that appeared to be colored with permanent marker, according to a post shared on the organization's Facebook page.
The West Yorkshire Police told BuzzFeed News that officers dropped the kittens off at the center for care.
But he was unable to provide further information about where they were found and who may have marked them.
Katie Jane, a volunteer with the center, called it "a dreadful act of cruelty" on Facebook, adding it is unclear what "damage this may have caused."
Jane told the BBC the 4-week-old kittens, which she named Smurf and Shrek, have been making "marvelous progress."
She has been feeding the two kittens every four hours and consulted with a veterinary poison information service about how to remove the ink safely.