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: an automobile engine transforms chemical energy into mechanical energy. 
Sentence2: cars transform chemical energy into mechanical energy.
Example Output: chemical

Example Input: Sentence1: an animal requires warmth for survival. 
Sentence2: Light and heat and warmth are basic necessities for survival.
Example Output: warmth

Example Input: Sentence1: Cytoplasm refers to all of the cellular material inside the plasma membrane. 
Sentence2: Cytoplasm refers to all of the cellular material inside the outer membrane.
Example Output:
Cytoplasm