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.

Ex Input:
Sentence1: All lizards are reptiles. 
Sentence2: Lizards are tetrapod vertebrates that produce amniotic eggs.

Ex Output:
lizards


Ex Input:
Sentence1: keeping food cold is used for keeping food fresh. 
Sentence2: Keeping food at 40 degrees F or lower is used for keeping food fresh.

Ex Output:
food


Ex Input:
Sentence1: Condensation is the reverse of vaporization , or change from liquid to gas. 
Sentence2: The reverse of vaporization changes a gas into a liquid by reducing heat energy.

Ex Output:

reverse