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: if fossils of a water animal or plant are found in a place then that place used to be covered by water in the past. 
Sentence2: Common fossils include plant fossils like ferns.

Ex Output:
plant


Ex Input:
Sentence1: Mad Cow disease is a concern. 
Sentence2: pathogens can cause Mad Cow.

Ex Output:
Cow


Ex Input:
Sentence1: a switch is used to start the flow of current in an electrical circuit. 
Sentence2: With switch closed, electricity flows through wires, switch and bulb, to light up the bulb.

Ex Output:

switch