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: Any antigen that causes an allergy is called an allergen. 
Sentence2: molds are antigens.
antigen

Sentence1: boiling is when liquids are heated above their boiling point. 
Sentence2: If the pressure is reduced, the boiling point is lowered.
boiling

Sentence1: Every kid has a bicep and a tricep muscle that is visible. 
Sentence2: muscle contracting causes a person 's elbow to straighten.

muscle