What does it mean for a reed to look like a mountain?

The tip of the reed is typically lined up flush with the tip of the mouthpiece, but in some cases, depending on the player, there may be very slight variations (of up to around 0.3 mm). There can also quite a bit of difference from player to player when it comes to the position of the ligature, but it is usual to attach and tighten it down below the point of the reed where the slope stops.
When a reed is held up to the light, light passes through the thinner, transparent part, making it brighter, and the thicker parts that light does not pass through look darker. There are those who say that for good reeds, this thicker, dark part of the reed, the heart, should look something like a symmetrical mountain.