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: Herbs are medicines and aids. 
Sentence2: herbs are used for curing people when they are sick.

Ex Output:
Herbs


Ex Input:
Sentence1: Centrioles come in pairs. 
Sentence2: Something that comes in pairs are organelles involved in cell division.

Ex Output:
come


Ex Input:
Sentence1: Like a mushroom, it lacks chlorophyll and is nonphotosynthetic. 
Sentence2: Mushrooms are nonphotosynthetic and cannot make food to grow.

Ex Output:

mushroom