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: an earthquake causes the ground to shake. 
Sentence2: A number of buildings in Istanbul also were damaged in the earthquake.

Ex Output:
earthquake


Ex Input:
Sentence1: Plants release oxygen during the day but not during the night. 
Sentence2: ferns release oxygen during the day but not during the night.

Ex Output:

day