instruction:
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.
question:
Sentence1: Sound vibrations can be compared to pond ripples. 
Sentence2: dropping an object into water causes pond ripples.
answer:
pond


question:
Sentence1: protein is used to repair cells by the human body. 
Sentence2: Wound healing requires protein.
answer:
protein


question:
Sentence1: Fish, such as tuna, is a high protein food. 
Sentence2: tuna have a circulatory system with a two-chambered heart.
answer:

tuna