As the donkey was “unclean,” it would not be eaten except in the last resort; and its head would be its worst and cheapest part.
Cab - This measure is not mentioned elsewhere in Scripture. According to the rabbinical writers it was the smallest of all the dry measures in use among the Jews, being the sixth part of a seah, which was the third part of an ephah. If it was about equal to two of our quarts, the “fourth part of a cab” would be about a pint.
Dove’s dung - Most commentators understand by this expression a sort of pulse which is called “dove’s dung,” or “sparrow’s dung” in Arabic. But it is possible that the actual excrement of pigeons is meant. The records of sieges show that both animal and human excrement have been used as food - under circumstances of extreme necessity.