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: Amphibians have permeable skin that easily absorbs substances from the environment. 
Sentence2: Some substances are harmful to the body and block biological systems.

A: substances
****
Q: Sentence1: Eggs are usually laid in a nest. 
Sentence2: birds have nests.

A: nest
****
Q: Sentence1: Viruses are usually considered to be nonliving. 
Sentence2: Variola major, the virus that causes smallpox, is considered a potential bioterrorism agent.

A:
Viruses
****