1.) "he is lying on his side." - "his side" means the left or right side of his body. so he is lying with either the left or the right side of his body on the floor (or whatever he is lying on). As opposed for example to "he is lying on his back." where he would be lying with his "backside" down. 2.) no, gooses dont eat sauce, but they are being eaten with sauce. so when the sauce matches with the goose it will match with the gander too. this is a phrase you use to suggest that if a particular type of behaviour is acceptable for one person, it should also be acceptable for another person, or "what is good for one person is good for another."

If you lie on your side then your hip, arm and ear are in contact with the mattress (or whatever you are lying on). Your back is not in contact. Your fact and front are not in contact. "Sauce for the goose" is not referring to what the goose would eat. It is referring to what would be put onto a cooked goose (or gander) to eat it-- at least that is my understanding. What the saying means is a general statement that what is good for the female is also good for the male (and probably the other way around also). It does not necessarily have anything to do with eating (or being eaten).