Jamieson, Fausset and Brown on 1 Samuel 9:24

24. the cook took up the shoulder ... and set it before Saul. And Samuel said, Behold that which is left; set it before thee, and eat--that is, reserved (see on Ge 18:7; Ge 43:34). This was, most probably, the right shoulder; which, as the perquisite of the sacrifice, belonged to Samuel, and which he had set aside for his expected guest. In the sculptures of the Egyptian shambles, also, the first joint taken off was always the right shoulder for the priest. The meaning of those distinguished attentions must have been understood by the other guests.