I'm reading a book on helium

This joke really takes off thanks to a clever pun, specifically playing on the word "uplifting." The humor comes from its double meaning: if a book were literally made of or filled with helium, you couldn't put it down because it would float away, constantly moving upward. But "uplifting" also describes something inspiring, positive, or morale-boosting, suggesting the book's content is truly fantastic and makes you feel good. It’s a delightful blend of physical properties and metaphorical appreciation.

Helium is a truly fascinating element, famous for being the second lightest element in the universe. First detected in the sun's spectrum before being found on Earth, this noble gas is lighter than air, which is why it makes party balloons float and blimps soar. Its unique lightness is what makes this joke fly, giving a nod to its literal "upward" tendency while also praising a great read that lifts your spirits.