2/5 Draw Bend to F Octave
Here's a little known fact...
If you play 2 draw and 5 draw at the same time (blocking holes 3 and 4 with your tongue... a standard octave embouchure size) you get G on the bottom (2 draw) and F on the top (5 draw). This creates a great bluesy dissonance that's used often by players.
You probably already knew this, BUT, did you know you can bend the 2 draw G down to F, without affecting the 5 draw F, creating an F octave?
Practice a tongue blocked 2 draw bend a couple of times before you give this a try. Make sure to not use any mouth or auxiliary muscle tension, it needs to be all tongue movement. Now play your 2/5 (C Harmonica is the easiest for most people) and focus on creating the same bend and the 2 will drop to 2" while the 5 draw remains at pitch.
Now you know how to impress other harmonica players at a party.