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: Lancelet larvae are free-swimming. 
Sentence2: some larvae lack a hardened backbone.

Ex Output:
larvae


Ex Input:
Sentence1: Heat and temperature are the same. 
Sentence2: a thermometer is used to measure heat.

Ex Output:
Heat


Ex Input:
Sentence1: sonar is used to find the location of an object. 
Sentence2: Bats use echolocation which is like sonar.

Ex Output:

sonar