What did Rene use to bite his brother?

The reason "His teeth" is the correct answer lies in the common understanding of what it means to bite. Biting specifically involves using the teeth to come into contact with another object or person, typically in a way that can cause pain or is aggressive. In this context, when the question asks what Rene used to bite his brother, it is implied that the act of biting would logically require the use of teeth, as they are the anatomical parts designated for such action. Other options, like hands, words, or nails, do not align with the physical act of biting as they serve different functions. Hands could grasp or hold but cannot bite, words refer to verbal communication that cannot physically affect another person in the way biting does, and nails, while they can scratch or claw, do not represent the traditional action of biting. Thus, "His teeth" is the most appropriate and accurate choice.