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.

[EX Q]: Sentence1: Lions live in social groups called prides. 
Sentence2: Chimpanzees live in social groups called communities.
[EX A]: groups

[EX Q]: Sentence1: If there is sun, there is sunlight, there is day. 
Sentence2: Energy enters ecosystems from the sun.
[EX A]: sun

[EX Q]: Sentence1: matter vibrating can cause sound. 
Sentence2: Sound causes it to move like the head of a drum.
[EX A]:
sound