From the Super Mario Wiki
Teehee Butterflies are flying butterfly insects that appear in Yoshi's Story. They fly around and regularly change color from pink to blue. Eating a pink one restores a Yoshi's life and eating a blue one makes it go down, as it is said by a Hint Block that the blue ones taste bitter.
The name of this enemy comes from the noise they make when they change colors ("Teehee!") The Teehee Butterflies share their name with Teehee Valley from Mario & Luigi: Superstar Saga. However this is most likely just a coincidence.
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