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: Plants that shed their leaves seasonally each year are called deciduous plants. 
Sentence2: vines shed their leaves seasonally each year.
Example Output: each

Example Input: Sentence1: igneous rocks are formed from magma cooling. 
Sentence2: magma solidifies into igneous rocks.
Example Output: magma

Example Input: Sentence1: Humans have collected and grown mushrooms for food for thousands of years. 
Sentence2: Humans have collected and grown types of fungus for food for thousands of years.
Example Output:
Humans