Kommentar zu Bereschit 43:32

כי תועבה היא FOR THAT IS AN ABOMINATION — it is a hateful thing to the Egyptians to eat together with the Hebrews. Onkelos states a reason for this.

כי תועבה, something so abhorrent to the Egyptians that they would spit out when observing such a “barbaric” way of eating meat. We know from other sources also that the Egyptians were of a very haughty disposition as mentioned for instance by Isaiah 30,7 קראתי לזאת רהב הם שבת, “truly, I call this, ‘they are a threat that has ceased.’” [the prophet calls Egypt a ‘paper tiger’ in his time. Ed.] The Egyptians’ attitude to people whose vocation was to tend flocks was one of utter disdain, as we know from 46,34. They had contempt for sheep and goats, hence their contempt transferred itself to the people raising such animals. This attitude to sheep and goats is mirrored when Moses asks Pharaoh how he could expect the Israelites to slaughter such animals while in Egypt without running the risk of the local populace stoning them to death for doing this. (Exodus 8,22) Stoning someone to express one’s disgust with his conduct is nothing new; we encounter it in Samuel II 16,5-6 when Shimi ben Geyrah, not only cursed (king) David publicly, but also threw stones at him.

וישימו לו לבדו, in order that his brothers should not notice that he too was a Hebrew.