Lets say you have to pick between the two. You [i]will[/i] get attacked one way or the other but which would you prefer? You can't just be like "Nuh im 2 cool 4 sherks or allgatres"
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alligator. either i can grapple its mouth shut, or i go quick. with a shark you can only punch it at just the right spot on its nose and thats all you can do. you would never be able to generate the sufficient force to break its bones while underwater.