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: Heat production is increased by shivering and non-shivering thermogenesis . 
Sentence2: Heat production occurs when many muscles contract a little bit all at once.
Example Output: Heat

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

Example Input: Sentence1: a pan is used for cooking food by heating food in it on a stove. 
Sentence2: Fire puts off heat.
Example Output:
heating