Furballs are small furry humming creatures the same color as custard. These creatures were available for sale in the Magical Menagerie in Diagon Alley (PA4).
Commentary
Notes
They were probably Puffskeins, which are also custard-colored and emit a humming sound, but Harry was probably not familiar with the name at the time.
From the Web
"Puffskein" from Harry Potter Wiki
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