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.

Ex Input:
Sentence1: Streams may start with runoff or water seeping out of a spring.
Sentence2: Most water comes from precipitation.

Ex Output:
water

Ex Input:
Sentence1: a seismometer is used to measure the strength or magnitude of an earthquake.
Sentence2: Seismometer Calibration : Instructions on how to calibrate a homemade seismometer.

Ex Output:
seismometer

Ex Input:
Sentence1: Muscles can only contract.
Sentence2: Smooth muscles are involuntary muscles.

Ex Output:
Muscles