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.

Example 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.
Example Output: bright

Example Input: Sentence1: friction causes the temperature of an object to increase. 
Sentence2: internal combustion engines get hot.
Example Output: temperature

Example Input: Sentence1: Insects are the most common invertebrates. 
Sentence2: most insects have a nervous system.
Example Output:
Insects