Generate an overlapping word between the given two sentences. When you find the overlapping words, they don't have to match exactly, e.g., "survival" and "survive" are valid overlapping words. Little words like "the" or "of" don't count! You must generate significant words which are not the stop words.

Q: Sentence1: a battery converts chemical energy into electrical energy. 
Sentence2: A battery produces a flow of electrons.

A: battery
****
Q: Sentence1: sharpening an object causes that object to change shape. 
Sentence2: sharpening a knife causes it to change shape.

A: causes
****
Q: Sentence1: Bighorns have hollow hair that traps body heat. 
Sentence2: bighorns' hollow hair prevents heat loss.

A:
Bighorns
****