Slipper is American as well. What she is doing is called "splatting". Normally they will do this if extremely relaxed and content. HOWEVER! It is also a sign of being too hot. Especially if she is panting or has her tongue out she is too hot. Go with your gut feeling. If you think she is too hot she is. Some do not have the common sense as you say and have been burned so it is best to maybe put another layer of fabric under the slipper or redo your set up.