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: an animal requires air for survival. 
Sentence2: It is breathed in by animals and restored to the air by the photosynthesis mechanism of plants.

Ex Output:
air


Ex Input:
Sentence1: Telephone Telephone calls are expensive. 
Sentence2: Communicating by transmitting sound is expensive.

Ex Output:
expensive


Ex Input:
Sentence1: chemical splashing can cause harm to humans. 
Sentence2: Toxic materials that splash on a human can cause harm.

Ex Output:

splashing