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.

[EX Q]: Sentence1: Any antigen that causes an allergy is called an allergen. 
Sentence2: Antigens are proteins foreign to the body.
[EX A]: antigen

[EX Q]: Sentence1: Mangoes are propagated vegetatively and by seeds. 
Sentence2: animals propagate mangoes.
[EX A]: Mangoes

[EX Q]: Sentence1: Insects may live in large colonies and have complex social behaviors. 
Sentence2: Insects are the only arthropod to have wings.
[EX A]:
Insects