Given the task definition, example input & output, solve the new input case.
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: Sentence1: pesticides cause pollution. 
Sentence2: pollution can harm animals.
Output: pollution.
The word "pollution" is common to Sentence1 and Sentence2. So, it's a good answer.

New input case for you: Sentence1: blowing air into a whistle causes air to vibrate inside the whistle. 
Sentence2: If the persist, blow a whistle loudly into the mouthpiece.
Output:
whistle