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: Interestingly, a squid is also a mollusk. 
Sentence2: squids have a circulatory system with one or two hearts that pump blood.

A: squid
****
Q: Sentence1: Hydrogen bonds cause water to expand when it freezes. 
Sentence2: Hydrogen bonds Hydrogen bonds are primarily electrostatic in origin.

A: Hydrogen
****
Q: Sentence1: Most mollusks have shells. 
Sentence2: Cephalopods are a class of marine mollusks.

A:
mollusks
****