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: Some birds are pollinators that co-evolved with plants. 
Sentence2: insects pollinate plants.

Ex Output:
plants


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

Ex Output:
Mating


Ex Input:
Sentence1: a freezer is used for cooling things. 
Sentence2: Freezer for fish is also provided.

Ex Output:

freezer