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: a sifter is used for separating mixtures. 
Sentence2: a sifter is used for some recipes.
Example Output: sifter

Example Input: Sentence1: Endospores are commonly found in soil and water. 
Sentence2: Some bacteria form resistant cells called endospores.
Example Output: Endospores

Example Input: Sentence1: a beak is used for catching prey by some birds. 
Sentence2: Worms are prey for birds.
Example Output:
prey