What is the effect of O'Connor's comparison of the grandmother to a "parched old turkey hen crying for water?"

O'Connor makes this comparison when the grandmother is about to be killed by the Misfit. Turkey hens often make calls, which sound like yelps, when they are summoning their young. Therefore, the effect of comparing the grandmother to an old turkey hen is to emphasize her fruitless call for her son, Bailey. She calls to her son to help her (and perhaps in part because she knows that he is likely dead), but there have already been several pistol reports from the woods where the Misfit's two accomplices have taken the rest of the family, including Bailey, his wife, and children. It's clear, then, that Bailey can not help his mother. The comparison of the grandmother to the turkey hen also makes her seem helpless and like a sacrificial victim, as a turkey hen can easily be led to slaughter, despite its cries.