"Kittens knead on their mothers while nursing," Rachel Barrack, veterinarian of Animal Acupuncture in New York City, told The Dodo. "Many cats carry this behavior into adulthood and may knead their owners, other furry siblings or bedding."
Barrack said that cats are soothed by kneading, and can even enter "a trancelike state."
"We refer to kneading cats as 'muffin-makers' and 'biscuit-bakers,'" Katie Armour, project coordinator at MSPCA Boston Adoption Center, told The Dodo. "Nursing kittens knead their mom's teats as they suckle to stimulate lactation, and they purr to let her know that they're happy and are getting full bellies."
While most cats keep purring throughout their lives, not all cats actually keep kneading beyond kittenhood, according to Armour. But many continue - and some get really into it. Some cats get so into their kneading trances that they even start drooling. And there's actually a sort of heartbreaking reason for the dribble.
"In my experience, this is often seen with orphaned kittens who were bottle-fed by humans, or kitties who were weaned too young," Armour said. "They still have that vestigial connection between kneading and suckling that many other cats have outgrown."