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: Eggs are usually laid in a nest. 
Sentence2: birds have nests.
Example Output: nest

Example Input: Sentence1: If there is sun, there is sunlight, there is day. 
Sentence2: Energy enters ecosystems from the sun.
Example Output: sun

Example Input: Sentence1: Bacteria are destroyed by cooking heat. 
Sentence2: cooking food removes bacteria.
Example Output:
Bacteria