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: Precipitation falls on the windward side of the mountain range. 
Sentence2: Sheep tend to favour the windward side of a paddock.

Ex Output:
windward


Ex Input:
Sentence1: Adaptation traits contribute to individual fitness and to the evolution of animal genetic resources. 
Sentence2: Behaviors can improve the evolution of animal genetic resources.

Ex Output:
animal


Ex Input:
Sentence1: a plant requires photosynthesis to grow. 
Sentence2: Bamboos are vigorous, rugged plants.

Ex Output:

plant