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: Proper digestion is vital for nutrient absorption. 
Sentence2: Digestion is important for an animal's survival.
digestion

Sentence1: microbial fuel cells convert chemical energy into electrical energy. 
Sentence2: microbial fuel cells convert chemical energy into kinetic energy.
cells

Sentence1: a compass is used for determining direction. 
Sentence2: A compass is used for determining velocity and intent.

compass