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: Scientists still know relatively little about Archaea. 
Sentence2: scientists still know relatively little about non-bacterial prokaryotes.

Ex Output:
Scientists


Ex Input:
Sentence1: creating paper requires cutting down trees. 
Sentence2: Trees begin as epiphytes on host trees.

Ex Output:
trees


Ex Input:
Sentence1: Cows are social animals. 
Sentence2: when a cow moves, chemical energy is converted to mechanical energy.

Ex Output:

Cows