From the Super Mario Wiki, the Mario encyclopedia
A Surprise Ball (also known as a ! Ball or ‘!’ Block) is a spherical platform that Baby Yoshis use during the events of Yoshi's Story. Surprise Balls are round in shape and float in midair. To use one, the Yoshi must use his tongue on this object, and he will be pulled in and thrust upwards, ending up standing on top of it.
A similar looking item exists in the game, titled the ? Bubble–instead of an exclamation mark, this red ball has a white question mark on it.
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