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: when electricity flows to a light bulb , the light bulb will turn on. 
Sentence2: water pumps can turn on light bulbs.
Example Output: bulb

Example Input: Sentence1: Streams may start with runoff or water seeping out of a spring. 
Sentence2: streams may start with runoff or h2o seeping out of a spring.
Example Output: Streams

Example Input: Sentence1: an image in a mirror is formed by reflecting light. 
Sentence2: an image in a mirror is formed by reflecting rays or beams.
Example Output:
formed