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.

Sentence1: Caverns Secrets are hidden in caves. 
Sentence2: hidden caves are formed by carbonic acid in groundwater seeping through rock and dissolving limestone.
are

Sentence1: Cnidarians have a hydrostatic skeleton. 
Sentence2: Jellyfish have a hydrostatic skeleton.
hydrostatic

Sentence1: Cell Division Cell Division Cell division is the method used by cells to reproduce. 
Sentence2: the method used by cells to reproduce is how organisms grow and repair themselves.

cells