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.

Q: Sentence1: Leeches are external parasites. 
Sentence2: Leeches live on the surface of their hosts.

A: Leeches
****
Q: Sentence1: Finally, the fluid in the nephron reaches a collecting duct . 
Sentence2: fluid in the kidneys collect into ducts.

A: fluid
****
Q: Sentence1: Menopause occurs when menstruation stops occurring, usually in middle adulthood. 
Sentence2: It is considered premature for menstruation to stop before age 40.

A:
menstruation
****
