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.

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

A: Chordates
****
Q: Sentence1: Ice is frozen water. 
Sentence2: ice expands.

A: Ice
****
Q: Sentence1: Some species of reptiles can go several weeks between meals. 
Sentence2: Meat-eating reptiles can live with any source of light, natural or artificial.

A:
reptiles
****