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: Insects have 2 antennae. 
Sentence2: Insects have 2 appendages to detect sound.

A: 2
****
Q: Sentence1: An astronaut is a scientist who is a space explorer. 
Sentence2: Space explorers require preserved food for long flights.

A: explorer
****
Q: Sentence1: Unlike most female animals, which have two functioning ovaries, the chicken usually has only one. 
Sentence2: Something chickens have only one that functions is used in reproduction.

A:
chicken
****