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.

Sentence1: hearing is used for sensing sound by animals. 
Sentence2: functioning ears are used for sensing sound by animals.
animals

Sentence1: Erosion of rock makes nutrients available. 
Sentence2: rain causes nutrients to be available.
nutrients

Sentence1: Many ethologists capture their observations on videotape or audio tape. 
Sentence2: Scientists who study how animals behave use videotape or audio tape.

audio