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: gills are used for breathing water by aquatic animals. 
Sentence2: gills are used for breathing water by sharks.
are

Sentence1: Leeches are external parasites. 
Sentence2: Leeches live on the surface of their hosts.
Leeches

Sentence1: Forest fires are examples of wildfires. 
Sentence2: Lightning can cause a wildfire.

wildfires