Forgot about this cute little story:

It used to be that when you dragged an item off the Dock and dropped it, the icon would disappear in a puff of smoke and make a satisfying noise. The animation was strangely primitive against the backdrop of the slick user interface of what used to called Mac OS X.

I too wondered why that animation was weirdly amateurish, almost like a placeholder. Well,

One of the most talented engineers on the team took out a piece of paper. I wish I could say it was a napkin to make the story better. ¶ On the piece of paper, he drew a series of five frames. The intention of the designer was that these drawings would stoke further discussion. That it would get cleaned up and refined later. ¶ But that never happened. It shipped as is. And the rest is history.

Also when looking it up, I found a mention of a fascinating bug that exposed the origin of the animation as a sprite.