Boos are enemies (and sometimes allies) that appear in lots of Yoshi games as bad guys, but in a few of them, there are good guys. There is one good one known as Heater Boo Han. Boos cover their faces when you look at them, but advance upon you when you turn your backs on them. But this does not happen in most Yoshi Boo games.
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What happend to this Yoshi when he got into a so called staring contest with a Boo