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: Instead, the body is covered with a protective shell of bony armor. 
Sentence2: Most mollusks have protective of bony armor.

Ex Output:
armor


Ex Input:
Sentence1: Clouds are one form of condensation. 
Sentence2: Clouds are one form of changing from a gas into a liquid by reducing heat energy.

Ex Output:
Clouds


Ex Input:
Sentence1: Insects generally have two pairs of wings for flight. 
Sentence2: Many insects have wings, but arachnids have no wings.

Ex Output:

Insects