I had a cat who did that! Whenever someone was petting him and he got really blissed-out, he would seem to mentally revert to baby kitten status, and start doing that kneeding thing with his paws & sucking on a blanket, or the person’s shirttail, or whatever. It was sort of adorable at first, but it got kinda gross & annoying; I didn’t want my shirt soaked with cat spit! I would try to get him to snap out of it, but he kept starting it up again. I wonder now if he was never properly weaned.He was a great cat, though. Been gone 15 years, and I still miss him.