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: Eggs are usually laid in a nest. 
Sentence2: birds have nests.
nest

Sentence1: Lenses are used in cameras, microscopes, binoculars and many other optical equipment. 
Sentence2: lenses are used for observing materials up close.

Lenses