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: Dromaeosaurs are part of the theropod group of dinosaurs. 
Sentence2: Birds evolved from a group of bipedal dinosaurs that included Dromaeosaurs.
Example Output: Dromaeosaurs

Example Input: Sentence1: a flower 's purpose is to produce seeds. 
Sentence2: producing seeds allows seed to germinate in the spring so the plant can grow.
Example Output:
produce