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

Example Input: Sentence1: Sand and mud are examples of sediments. 
Sentence2: layers of sand over the remains of organisms over time can create fossils.
Example Output: Sand

Example Input: Sentence1: Viruses are not cells at all, so they are neither prokaryotes nor eukaryotes. 
Sentence2: influenza is not a cell.
Example Output:
cells