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: Caverns Secrets are hidden in caves. 
Sentence2: hidden caves are formed by carbonic acid in groundwater seeping through rock and dissolving limestone.

A: are
****
Q: Sentence1: Polyps usually reproduce asexually. 
Sentence2: Polyps usually reproduce several different ways.

A: Polyps
****
Q: Sentence1: Snails and slugs are invertebrates. 
Sentence2: snails lack a vertebral column.

A:
Snails
****