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: Sentence1: pesticides cause pollution. 
Sentence2: pollution can harm animals.
Example solution: pollution.
Example explanation: The word "pollution" is common to Sentence1 and Sentence2. So, it's a good answer.

Problem: Sentence1: an animal usually requires a warm body temperature for survival. 
Sentence2: Warm blooded animals have a constant body temperature.

Solution: animal