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: Human mating behavior also involves some competition. 
Sentence2: Human mating may lead to aggressive behaviors or displays of aggresion.

Ex Output:
Human


Ex Input:
Sentence1: Protozoa make humans sick when they become human parasites. 
Sentence2: paramecium are single celled animals that make humans sick when they become human parasites.

Ex Output:
become


Ex Input:
Sentence1: when the seasons change from the summer to the fall , the amount of daylight will decrease. 
Sentence2: when the seasons change from the summer to the fall, sheep breed more.

Ex Output:

change