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


[Q]: Sentence1: Lymph is a fluid that leaks out of capillaries into spaces between cells. 
Sentence2: Humans are made up of trillions of cells.
[A]: cells


[Q]: Sentence1: rocks interacting with wind over long periods of time causes weathering. 
Sentence2: Smaller rocks come from the breakage and weathering of bedrock and larger rocks.
[A]:
weathering