Hot Bottle of Arm

A scientific amount of heat equal to the thermal output of one (1) arm, warm enough to attract the companionship of a small-to-medium sized pet snake.

The term comes from the comparison of one's own arm to a large bottle of hot water.

"Of course cats and small reptiles love her so much, shes got two hot bottles of arm."

Jane: You feel a little warm, are you alright?
Timothy: It's fine, I just have a whole hot bottle of arm