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: a battery converts chemical energy into electrical energy. 
Sentence2: A battery produces a flow of electrons.

A: battery
****
Q: Sentence1: All lizards are reptiles. 
Sentence2: Lizards are tetrapod vertebrates that produce amniotic eggs.

A: lizards
****
Q: Sentence1: Constriction occurs when the muscular walls of blood vessels contract. 
Sentence2: Tight squeezing ccurs when the muscular walls of blood vessels contract.

A:
blood
****