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: Sound vibrations can be compared to pond ripples. 
Sentence2: dropping an object into water causes pond ripples.

Answer: pond


Question: Sentence1: friction causes the temperature of an object to increase. 
Sentence2: Friction causes the temperature of a toy to increase.

Answer: causes


Question: Sentence1: the Earth being tilted on its rotating axis causes seasons. 
Sentence2: The Earth being tilted on its rotating axis causes lake level changes.

Answer:
Earth