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

Example Input: Sentence1: Streams may start with runoff or water seeping out of a spring. 
Sentence2: streams may start with runoff or h2o seeping out of a spring.
Example Output: Streams

Example Input: Sentence1: Some animals, like moles and earthworms spend their entire lives underground. 
Sentence2: Moles reside below the surface so that animal will be protected from a wild fire.
Example Output:
moles