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: boiling means change from a liquid into a gas by adding heat energy. 
Sentence2: boiling changes a liquid into steam.
Example Output: liquid

Example Input: Sentence1: friction causes the temperature of an object to increase. 
Sentence2: When we increase the temperature of objects, they always expand.
Example Output: increase

Example Input: Sentence1: when the body is hot , sweat is produced to cool the body. 
Sentence2: The evaporation of sweat occurs when a body is hot.
Example Output:
body