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: Genetics is the study and application of principles of inheritance to plants and animals . 
Sentence2: Pedigrees are useful tools for studying Genetics.
Example Output: Genetics

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

Example Input: Sentence1: extreme heat and pressure change rock into metamorphic rock. 
Sentence2: Metamorphic Rocks Metamorphic Rocks Metamorphic rocks are formed by pressure and heat.
Example Output:
metamorphic