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: a fire requires oxygen to burn. 
Sentence2: A fire requires something with exactly eight protons to burn.
burn

Sentence1: Flies are insects with two wings. 
Sentence2: Flies are arthropods with two wings.
Flies

Sentence1: Frostbite is the freezing of body parts. 
Sentence2: Reducing heat energy of body parts results in frostbite.

Frostbite