My dog is addicted to crack

Ass crack, that is.
How come little dogs like to curl up in the crack of your ass when they are under the covers? Usually, Sheena is snuggled up to Hubs, but lately she seems to favor me. Even when I'm curled up on the couch, she will wedge her way into the triangular space between the back of my knees and my butt. If I get up from the couch, she will dive into the space between the cushions, until another butt crack is available. Weird little dog.