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 animal usually requires a warm body temperature for survival. 
Sentence2: Warm blooded animals have a constant body temperature.
Example Output: animal

Example Input: Sentence1: Polygenic inheritance Polygenic traits are controlled by an unknown number of genes. 
Sentence2: Skin color is inherited from a number of genes.
Example Output: genes

Example Input: Sentence1: Fungi are involved in decomposition, as well. 
Sentence2: Fungi increase the amount of organic matter in soil.
Example Output:
Fungi