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: Organisms cluster around hydrothermal vents in the ocean floor. 
Sentence2: vents on the ocean floor are powered by heat.
Example Output: vents

Example Input: Sentence1: Mitosis is cell division. 
Sentence2: Chromosomes are the form of the genetic material of a cell during mitosis.
Example Output: Mitosis

Example Input: Sentence1: Differentiation is the process by which unspecialized cells become specialized. 
Sentence2: Neurones are highly specialized cells.
Example Output:
cells