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.

Input: Consider Input: Sentence1: dropping an object into water causes vibrations in the water.
Sentence2: Dropping an object into lake causes vibrations.

Output: dropping

Input: Consider Input: Sentence1: Acid rain is precipitation which pH is 5.7 or lower.
Sentence2: gases from burning coal causes precipitation which pH is 5.7 or lower.

Output: 5

Input: Consider Input: Sentence1: Hearing is the act of perceiving sound.
Sentence2: the speed of hearing changes depending on the material passed through.
Output: Hearing