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.

Ex Input:
Sentence1: Echinoderms use pheromones to communicate with each other. 
Sentence2: Echinoderms are known for their round symmetry.

Ex Output:
Echinoderms


Ex Input:
Sentence1: if soil is permeable then water easily flows through that soil. 
Sentence2: if soil is permeable then h2o easily flows through the soil.

Ex Output:
flows


Ex Input:
Sentence1: Mutations may change the structure of a chromosome or just change a single nucleotide. 
Sentence2: Mutagenic chemicals may change the structure of a nucleotide.

Ex Output:

change