The onus in "bonus" is on "us"

This has absolutely nothing to do with breakable walls, I was just reminded of it when I was flipping between the Sonic 1 and Sonic 3 pictures in my previous post.

This is the sprite mapping layout for the HUD in Sonic 1. If you look at the S in "RINGS", you can see how each letter is aligned to the right, leaving a single pixel-wide gap on the left for spacing purposes.

To make the font italic in Sonic 2, the bottom half of each letter got dragged one pixel to the left. As a result, the S now spans the entire width of an 8x8 tile, but it looks okay because there's still a pixel of spacing overall.

When they removed the italics for Sonic 3 though, rather than starting from the Sonic 1 graphics, it seems they instead "straightened out" the Sonic 2 font: observe the bottom right corner of the S. As a side effect, all the text is now aligned to the left. Why does this matter? Because it screwed up the spacing on the "BONUS" mappings.

The "BONU" bit of the text happens to span the entirety of the 32 pixel-wide sprite, and counts on the leading space in the S to make the spacing work out. The S, as it turns out, is reused from the HUD graphics. When they aligned all the text to the left, they broke this spacing, and they never moved the "BONU" mapping over to compensate.

Got that? Okay, now go watch this considerably more interesting video.