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: bacteria cause food to spoil. 
Sentence2: Food poisoning occurs when spoiled food is eaten.

A: spoil
****
Q: Sentence1: heating an egg causes a chemical reaction in the egg. 
Sentence2: Insects hatch from eggs.

A: egg
****
Q: Sentence1: Echinoderms have a hydraulic system of locomotion called the water vascular system. 
Sentence2: Echinoderms have a hydraulic system of locomotion with tube feet.

A:
hydraulic
****