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: Amphibians have permeable skin that easily absorbs substances from the environment. 
Sentence2: Some substances are harmful to the body and block biological systems.
Example Output: substances

Example Input: Sentence1: Mating is generally preceded by courtship. 
Sentence2: Mating is generally similar across species.
Example Output: Mating

Example Input: Sentence1: Rain is liquid precipitation. 
Sentence2: rain increases moisture.
Example Output:
Rain