I recently finished a new website for my employer, a circus school. At the bottom, I included a little circus tent emoji to provide a visual coda to the footer, as well as a hidden Easter egg.
When you click on the tent, it sends confetti flying:
Few people will discover this effect on their own (though it does appear elsewhere on the site when you take actions like subscribing to the mailing list).
But for those who do happen to stumble across it and click on the emoji, they'll be rewarded for their curiosity and engagement.
In a culture that places so much value on efficiency and cheapness, unobtrusive bits of whimsy like this are a way to show your audience that you did more than just the bare minimum.
They're a way of thanking people for their attention by showing them that you put care into your craft and are proud to sign your work.
See also: Igniting Wonder