"A man should rather do work that is strange to him than have need of others." even if you need to skin an animal is the market in order to make a living there's a double meaning here-skinning an animal is already an unpleasant job, even at home how much more so if you have to do it in public, at the market at that time- there were butchers who would stand in some corner and people would bring their animals for him to slaughter and clean etc. it is unpleasant even in an enclosed setting- how much more so in the marketplace? it's embarrassing! so our sages say: "skin an animal in the marketplace and do not say, 