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: Heterotrophs are living things that cannot make their own food. 
Sentence2: food contains organic molecules.

Ex Output:
food


Ex Input:
Sentence1: Trees have woody stems covered with bark. 
Sentence2: Evergreens have woody stems covered with bark.

Ex Output:
bark


Ex Input:
Sentence1: Corals form large colonies in shallow tropical water. 
Sentence2: Something in the polyp stage can form large colonies in shallow tropical water.

Ex Output:

colonies