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.

[Q]: Sentence1: Methane gas is a produced by rotting compost, trash, and human waste. 
Sentence2: Methane gas can be produced by Slime molds.
[A]: Methane


[Q]: Sentence1: Heat production is increased by shivering and non-shivering thermogenesis . 
Sentence2: Heat production occurs when many muscles contract a little bit all at once.
[A]: Heat


[Q]: Sentence1: Characteristics of Reptiles Reptiles have backbones. 
Sentence2: Some species with backbones can go several weeks between meals.
[A]:
backbones