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: dropping an object into water causes vibrations in the water. 
Sentence2: Dropping an object into lake causes vibrations.

A: dropping
****
Q: Sentence1: creating paper requires cutting down trees. 
Sentence2: Trees begin as epiphytes on host trees.

A: trees
****
Q: Sentence1: an electrical insulator slows the transfer of electricity. 
Sentence2: Plastic slows the transfer of electricity.

A:
electricity
****