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: Boiling water can cause burns. 
Sentence2: heating water can cause burns.
Example Output: water

Example Input: Sentence1: Fission is a type of reproduction, but a baby is the result of sexual reproduction. 
Sentence2: the fallopian tubes are used to make babies.
Example Output: baby

Example Input: Sentence1: Mammals that are viviparous are called therian mammals. 
Sentence2: Whale sharks are called therian mammals.
Example Output:
are