Why did the biology book look so sad?

This joke hinges on a classic comedic device: wordplay, specifically a pun. The humor comes from the double meaning of the word "problems." In one sense, "problems" refers to the emotional difficulties or troubles that might make someone, or in this case, a book, feel sad. But in the context of a biology book, "problems" also directly refers to the exercises, questions, and challenges that students are expected to solve within its pages.

Anyone who's ever cracked open a textbook, especially in a subject like biology, can probably relate. These books are often packed with diagrams to label, experiments to analyze, and questions to answer at the end of each chapter. For many students, grappling with these numerous academic "problems" can certainly feel like a source of sadness or frustration, making the book itself seem burdened by the sheer volume of tasks it presents. It's a lighthearted jab at the sometimes-overwhelming nature of academic study.