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: skin is used for protecting the body from harmful substances. 
Sentence2: Acids are harmful to tissue.
[A]: harmful


[Q]: Sentence1: erosion causes a river to become deeper and wider. 
Sentence2: On the contrary, the NILE is the longest river in Africa.
[A]: river


[Q]: Sentence1: Most reptiles have good eyesight and a keen sense of smell. 
Sentence2: Bats have good eyesight and rely on vision for long-distance orientation.
[A]:
eyesight