What's the Name of That Book??? discussion

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The Song of the Zubble-Wump
SOLVED: Children's/YA
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SOLVED. Children's (Dr. Suess) book with Horton the elephant, the Grinch, & egg that hatches into a songbird w/ the most beautiful voice. Grinch wants egg/ songbird for himself but when it hatches, he is so sour inside that her voice hurts his ears. [s]
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I'm thinking that maybe it wasn't an original Dr. Seuss book, it could be it was a Dr. Seuss-inspired children's book. But I'm pretty certain it contained specific characters of his like Horton and the Grinch, and those would've been copyrighted. Unless it was a different elephant, not Horton, and the bad guy just looked like the Grinch.
If anyone has any info about this book, I'd really appreciate it!