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: Spikes are forceful the tidal waves of electric current. 
Sentence2: spikes come from tidal energy.

Ex Output:
Spikes


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: Mating is generally preceded by courtship. 
Sentence2: Crabs appear to go through an extensive courtship behavior before mating.

Ex Output:

Mating