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: sharpening an object causes that object to change shape. 
Sentence2: sharpening a knife causes it to change shape.
[A]: causes


[Q]: Sentence1: Mammalian predators include the coyote and bobcat. 
Sentence2: a coyote's teeth is important for digestion.
[A]: coyote


[Q]: Sentence1: a cavern is formed by carbonic acid in groundwater seeping through rock and dissolving limestone. 
Sentence2: Limestone caves are formed when acids attack and dissolve the calcite in limestone.
[A]:
formed