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: bacteria cause food to spoil. 
Sentence2: Food poisoning occurs when spoiled food is eaten.

Answer: spoil


Question: Sentence1: Fish are the first known true chordates. 
Sentence2: Fish are the first known animal with a backbone.

Answer: Fish


Question: Sentence1: Birds include gulls, waterfowl, birds of prey and garden birds. 
Sentence2: Gull eggs have hard shells made of calcium carbonate.

Answer:
gulls