Sans was giving himself some bone. He held it in his hands. It's quite a funny bone, unlike any of the others, but tibia honest, it's Sans's favourite. It makes the skeleton shiver when he rubs it, and he remembers how many people he gave the bone to. Men, women and children, all got to see, touch and feel the bone.
One of Sans's blue attack bones, as seen in genocide. What did you think it was?