When a bottom's toes curl when he's getting a good balls deep fuck it's that mix of incredible pleasure and pain from the long dick hitting the bottom of his asshole (or that bend up inside the rectum) and it's a deep erotic pressure that drives a bottom wild but scares him at the same time. It's like he wanted the dick to keep pounding him deep but was scared at the same time. It's a bottom's duty to give into a big dicked top and let him fuck him like he wants to. It's all about satisfying Daddy and letting him fuck you good, deep and hard.