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: Heterotrophs get food by eating other living things. 
Sentence2: fish eat other living things.
living

Sentence1: lightning can cause a forest fire. 
Sentence2: Lightning can cause a natural cycle in forests.
lightning

Sentence1: TRH stimulates the pituitary gland to produce thyroid-stimulating hormone, or TSH. 
Sentence2: TRH synthesis is regulated directly by thyroid hormones.

TRH