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: Most pituitary hormones control other endocrine glands. 
Sentence2: Hormones tell the ovaries to produce eggs.
Example Output: hormones

Example Input: Sentence1: a greenhouse is used to protect plants by keeping them warm. 
Sentence2: Flower size varies by plant.
Example Output: plants

Example Input: Sentence1: an animal requires stamina to succeed at physical activities. 
Sentence2: animal males are more energetic than females.
Example Output:
animal