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: a stopwatch is used to measure time. 
Sentence2: Time can be measured with a clock or watch.
Example Output: measure

Example Input: Sentence1: All monkeys are mammals. 
Sentence2: monkeys conserve body heat with their hair or fur.
Example Output: monkeys

Example Input: Sentence1: an acid changes the color of litmus paper from blue to red. 
Sentence2: Sour tasting things changes litmus paper from blue to red.
Example Output:
changes