Parts of the Tongue, Part 2 - Blade
The blade of the tongue is the front of the tongue, just behind the tip. This part of the tongue is used for tongue blocking an octave and for standard single-hole tongue blocking. When performing an octave, your lips surround four holes and with a very light tough, the natural convex shape of the blade of your tongue covers the middle two holes (if you press your tongue on the face of the harmonica too hard you’ll block all four holes, so a light touch is important). When performing the standard single-hole tongue block your lips are again surrounding four holes, but the tongue covers the three holes to the left, leaving the right-most hole to sound the single note. If you’re not able to block all three holes with the blade of the tongue, stick your tongue out and under the harmonica a bit more to access the tongue farther back, where it's wider (and thus blocks more holes).