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: Sperm had to swim from male to female reproductive organs for fertilization. 
Sentence2: If fertilized, the egg implants itself in the uterus.

Output: fertilization


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: the gravitational pull of the Moon on Earth 's oceans causes the tides. 
Sentence2: the gravitational pull of the Moon on Earth 's oceans causes currents.


Output: Earth