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.

[EX Q]: Sentence1: Flies are insects with two wings. 
Sentence2: Flies are arthropods with two wings.
[EX A]: Flies

[EX Q]: Sentence1: a mutation in the sex cells of a parent can cause a new trait to appear in the parent 's offspring. 
Sentence2: Traits are initiated by mutation and recombination.
[EX A]: mutation

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