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: the mass of a planet causes the pull of gravity on that planet. 
Sentence2: the mass of a planet is what causes things to have weight.

Answer: mass


Question: Sentence1: if fossils of a water animal or plant are found in a place then that place used to be covered by water in the past. 
Sentence2: Common fossils include plant fossils like ferns.

Answer: plant


Question: Sentence1: poisonous darts are used for defense by sea anemones. 
Sentence2: poisonous darts are used for protection by sea anemones.

Answer:
anemones