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: Temperature Scales Temperature is the energy of vibration. 
Sentence2: a thermometer is used to measure energy of vibration.
Example Output: energy

Example Input: Sentence1: Muscles can only contract. 
Sentence2: Contraction is a type of movement.
Example Output: contract

Example Input: Sentence1: Scales provide protection and camouflage. 
Sentence2: scales are used for camouflage by scaled animals.
Example Output:
camouflage