Parentage

I presume you are referring to the Bundren children: Darl, Cash, Dewey Dell, Jewel and Vardaman. Jewel is the child who is not fathered by Anse Bundren. Jewel is physically different from his siblings. We are told by Darl in Chapter 5-

'He is a head taller than any of the rest of us, always was.'

Darl certainly observes that he is treated differently by their mother too-

'...ma always whipped him and petted him more.'

Jewel refuses to accept that their mother is dying, which frustrates those around him.Darl taunts his brother with this knowledge, and with the knowledge of his illegitimacy-

'Jewel, I say. Who was your father, Jewel?'

Jewel isolates himself from the others, doing his duty but saying little.