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.

Input: Consider 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.

Output: air


Input: Consider Input: Sentence1: Most mammals have hair, or fur, covering their body. 
Sentence2: Most mammals have a body covering for keeping warm.

Output: body


Input: Consider Input: Sentence1: Invertebrates are animals who lack a backbone or spinal column. 
Sentence2: Vertebrate chordates have a spinal column.


Output: column