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: Flatworms Flatworms or Platyhelminthes include flukes, tapeworms, and turbellarians. 
Sentence2: Tapeworms belong to the phylum Platyhelminthes.
Example Output: tapeworms

Example Input: Sentence1: if an object is made of a material then that object has the properties of that material. 
Sentence2: An object is an item in the real world.
Example Output: object

Example Input: Sentence1: Some parasites kill their host, but most do not. 
Sentence2: Parasites include parasitic wasps, and certain flies and nematodes.
Example Output:
parasites