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: looking at bright objects has a negative impact on the eyes. 
Sentence2: Looking at bright objects have a negative impact on the retina.

Ex Output:
bright


Ex Input:
Sentence1: an animal usually requires a warm body temperature for survival. 
Sentence2: Warm blooded animals have a constant body temperature.

Ex Output:
animal


Ex Input:
Sentence1: Butterflies pollinate plants as they feed on nectar. 
Sentence2: butterflies pollinate plants.

Ex Output:

Butterflies