What’s wrong with the picture on the left? The bit is attached backwards so that the orientation of the mouthpiece is wrong.

With some bits, it can be difficult to tell the right way from the wrong way so it’s important to take a good look at it before putting it in your horse’s mouth. If the bit is oriented incorrectly, it can cause your horse pain.

Think about the shape of a horse’s mouth and how the bit fits into it. For the bit to sit properly it has to be oriented so that the curvature looks like a gentle U. This allows the bit to curve forward — it will drape on the horse’s tongue, not poke him in the palate and rest on the bars.

Here’s another view of the same bit.  In this angle you can see the curvature of the mouthpiece.