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: Cnidarians have a hydrostatic skeleton. 
Sentence2: Jellyfish have a hydrostatic skeleton.
Example Output: hydrostatic

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: the mass of a planet causes the pull of gravity on that planet. 
Sentence2: Earth Jupiter Jupiter's mass is 318 times greater than Earth's mass.
Example Output:
mass