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.
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Question: Sentence1: Sperm pass out of the body through the urethra. 
Sentence2: Sperm travel from the testicles through the vas deferens to the seminal vesicles and the prostate.

Answer: Sperm


Question: Sentence1: creating paper requires cutting down trees. 
Sentence2: Rainforests are destroyed by logging and all of the trees are cut down.

Answer: cutting


Question: Sentence1: When the flow speeds up, it can dig the river bottom, causing further erosion. 
Sentence2: when a river flows faster, it will create a deeper valley due to increased erosion.

Answer:
erosion