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: Hermit crabs use the shells of dead snails for homes. 
Sentence2: Hermits crabs use dead snails shells as their place to live.
Hermit

Sentence1: Chordates have a complete digestive system and a closed circulatory system. 
Sentence2: All chordates are vertebrates.
Chordates

Sentence1: Heat production is increased by shivering and non-shivering thermogenesis . 
Sentence2: Heat production occurs when many muscles contract a little bit all at once.

Heat