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: Some mollusks are nearly microscopic. 
Sentence2: Some squids are nearly microscopic.
Example Output: Some

Example Input: Sentence1: if a neutral atom loses an electron then an atom with a negative charge will be formed. 
Sentence2: Ice crystals that are formed have a negative charge.
Example Output: charge

Example Input: Sentence1: an automobile engine transforms chemical energy into mechanical energy. 
Sentence2: an automobile engine transforms chemical energy into sound.
Example Output:
an