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: creating paper requires cutting down trees. 
Sentence2: Trees begin as epiphytes on host trees.
Example Output: trees

Example Input: Sentence1: boiling is when liquids are heated above their boiling point. 
Sentence2: If the pressure is reduced, the boiling point is lowered.
Example Output: boiling

Example Input: Sentence1: gravity causes objects that have mass to be pulled down on a planet. 
Sentence2: Weight is measured when objects are pulled down by gravity.
Example Output:
down