Which innovative book packaging design technique, introduced in the early 2010s, used thermochromic ink that revealed hidden text or images when touched by warm hands?

Book packaging design has evolved dramatically over the centuries, from ancient scrolls to modern digital formats. Beyond mere protection, book covers and packaging have become an art form that significantly impacts sales and reader engagement. This trivia tests your knowledge about innovative book packaging designs that transformed the publishing industry and created new reading experiences.

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Heat-Reactive Covers (pioneered by Penguin Books for Ray Bradbury's Fahrenheit 451 special edition)
Augmented Reality Dust Jackets (first used by Scholastic for interactive children's books)
Water-Revealing Pages (popularized by McSweeney's Quarterly Concern experimental literature)
Sound-Embedded Covers (developed by Harper Collins for audiobook companion editions)