He plops down between my ankles, reclines majestically, and begins to groom.
Ben is not a quiet groomer. Some cats may settle their fur in silent dignity, but Ben slurps. And he chews his claws in a weird fashion, grabbing each claw between his teeth and yanking upward, so that it eventually slides out between his teeth with an audible click! (I have no idea why he does this. His claws aren't overgrown, he has no difficulty walking, he has a scratching post which he uses and a number of objects that he's not supposed to use but does anyway. Ben is an odd cat. Possibly he is honing them for ninja-slaying.) And in the course of grooming, as he leans far backward with each claw nibble or wiggles around to groom each part of his eighteen pound anatomy, he gradually inches north, in a process that I have dubbed "snugglecreep."
He may start out at my ankles, but by the time I fall asleep, he's generally wedged between and across my knees. His primary goal is apparently to maximize contact between cat and human (he is happiest when he can sit on someone's lap and put a paw out on somebody else) and he has calculated the optimal way to do this. Despite nearly a year of single life, I still sleep on one side of the bed. Ben's nefarious plan is to locate the exact center point this area, snugglecreep to it via a slug-like flexion of the trunk, and then curl up and assume the approximate density of lead.*
At some point in the middle of the night, I usually roll over on my side and pull my knees up, whereupon Ben wedges himself into the acute angle formed by the backs of my legs, a position which requires startling amounts of flex in the spine. Should I get up in the night to visit the restroom, get a drink of water, check on the weird noises coming from the birdfeeder or scribble down an idea about clipper ships made of giant beets, Ben will retain this position, requiring me to fit myself awkwardly back into bed around the cat. If I wish to straighten out, I am forced to sleep diagonally along the bed, at which point, after a few minutes, Ben will grumble and stretch out along my side.
On rare occasions where I attempt to sleep on my back the entire night, a disgruntled Ben will creep north until he can drape himself across my pelvis. I usually wake up in short order, as he has an uncanny ability to locate a human bladder and plant a pointy feline chin directly on it. (This also applies to naps, although he prefers to lay in the other direction on the couch, chin on human knees and one back foot planted squarely where it will cause a napping human the most discomfort.)
None of this is nearly so disturbing as when I sleep on my stomach, in which case Ben has a tendency to get up, stretch, lay down across my back and go back to sleep. He doesn't do the loud get-up-right-now purr, he genuinely seems to want to sleep like that, even if he has to plant his back feet on the mattress and practically sit up to get his front feet and head across my back. (Ben is a very large cat. At full extension he can cover my torso from crotch to collarbone, and so he can fit part of himself on my back most of the time.)
Cats are weird.
*The fact that science has not adequately studied the occasional super-heavy properties of Felinium is a black mark against modern research.