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: Cells are the microscopic building blocks of organisms. 
Sentence2: proteins are the building blocks of organisms.
organisms

Sentence1: Basically, heat is energy. 
Sentence2: Head hair is especially important in preventing energy loss from the body.
energy

Sentence1: Eggs are usually laid in a nest. 
Sentence2: birds have nests.

nest