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: Chordates have a complete digestive system and a closed circulatory system. 
Sentence2: All chordates are vertebrates.

Ex Output:
Chordates


Ex Input:
Sentence1: Mating is generally preceded by courtship. 
Sentence2: Mating is generally similar across species.

Ex Output:
Mating


Ex Input:
Sentence1: a compass is used to navigate oceans. 
Sentence2: You can navigate through the Pacific with a compass.

Ex Output:

compass