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: All sharks are predators. 
Sentence2: hiding can be used for avoiding sharks.

A: sharks
****
Q: Sentence1: Frequency is the measurable rate of that vibration. 
Sentence2: hitting an object causes the particles in that object to change frequency.

A:
Frequency
****