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.

Ex Input:
Sentence1: Mammals that are viviparous are called therian mammals. 
Sentence2: Mouse-sized viviparous mammals evolved by Jurassic times.

Ex Output:
Mammals


Ex Input:
Sentence1: Endocrine glands include the pituitary, thyroid, parathyroid, adrenal, pineal and thymus glands. 
Sentence2: Some pituitary hormones can control the thyroid gland.

Ex Output:
thyroid


Ex Input:
Sentence1: Cynodonts became more mammal-like as they continued to evolve. 
Sentence2: some therapsids became more mammal-like as they continued to evolve.

Ex Output:

became


