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.

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

Example Input: Sentence1: Cultivation is easier if soil is loose. 
Sentence2: soil with more oxygen is easier to cultivate.
Example Output: Cultivation

Example Input: Sentence1: Desertifcation can be caused by overgrazing, soil erosion, prolonged drought, or climate change. 
Sentence2: being exposed to wind can cause Desertifcation.
Example Output:
Desertifcation