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: Lions live in social groups called prides. 
Sentence2: Chimpanzees live in social groups called communities.
[A]: groups


[Q]: Sentence1: folding an object causes that object to change shape. 
Sentence2: Folding an object causes that object to transform.
[A]: causes


[Q]: Sentence1: Muscle contraction occurs when muscle fibers get shorter. 
Sentence2: muscles activate before fibers get shorter.
[A]:
fibers