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: folding an object causes that object to change shape. 
Sentence2: Folding an object causes that object to transform.
Example Output: causes

Example Input: Sentence1: smell is used for finding food by some animals. 
Sentence2: Food includes small rodents and birds.
Example Output: food

Example Input: Sentence1: Protozoa make humans sick when they become human parasites. 
Sentence2: Malaria parasites are transmitted by mosquitos.
Example Output:
parasites