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.

Sentence1: if an animal lives under ground then that animal will be protected from a wild fire. 
Sentence2: animals that live under ground in California will be protected from some natural disasters.
animal

Sentence1: If there is sun, there is sunlight, there is day. 
Sentence2: Energy enters ecosystems from the sun.
sun

Sentence1: Mammals conserve body heat with their hair or fur. 
Sentence2: Dogs, of course, are mammals.

Mammals