I held down some key for too long while I was thinking and the Mac bleeped at me to intimate that some mode had been triggered, analogous to StickyKeys or FilterKeys on Windows.
Now, whenever I click, a yellow circle appears around my cursor - some sort of accessibility feature to show where my cursor is on the screen, I assume.
I've looked all over through the accessibility and trackpad settings but can't find how to toggle it off again.
How can I disable this feature?