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And what happened, then? Well, in Whoville they say – that the Grinch’s small heart grew three sizes that day. And then – the true meaning of Christmas came through, and the Grinch found the strength of*ten Grinches, plus two!
— Narrator · How the Grinch Stole Christmas!

Behind the line May contain spoilers.
Our reading
An editorial interpretation.
The enlarged heart gives an inner change a visible, impossible size. Greater strength follows the discovery of Christmas’s meaning, linking generosity with renewed energy. The playful arithmetic makes the transformation exuberant: feeling differently changes what the Grinch is able and willing to do.
Context reviewed