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.

[EX Q]: Sentence1: hearing is used for sensing sound by animals. 
Sentence2: functioning ears are used for sensing sound by animals.
[EX A]: animals

[EX Q]: Sentence1: Basically, heat is energy. 
Sentence2: Head hair is especially important in preventing energy loss from the body.
[EX A]: energy

[EX Q]: Sentence1: having no natural predators increases population size. 
Sentence2: Hawks have no natural predators.
[EX A]:
natural