I was pretty surprised when my balalaika teacher said on Friday that we were going to practice flagellato. In turn, he was pretty surprised that I didn't appear to know what flagellato was. When he showed me, I realized that I did know what flagellato was – the problem is that we don't use the Italian word for it. This happens a lot: he's always asking me silly questions like, "Do you know what forte and piano mean?," because Russian and English don't borrow all of the same music terms from Italian, and it's hard to know which ones will be shared by the two languages. Anyway, flagellato is playing on the harmonics!
In this context, harmonics are the special spots on a string where, if you apply a light touch (not pressing the string all the way down like you do to play a normal note) and pluck just so, a high-pitched "ghost note" will sound. To explain rather vaguely, they have to do with dividing the string into even ratios like 1:1 or 1:3. (Yeah, physics was never my favorite subject.) Bassists use harmonics to tune their instruments, since you can get the same harmonic note by touching different spots on different strings. That way, you can tune your A and D strings to each other by playing a harmonic A on both of them and matching the pitch.
So the exciting thing here is that there's a balalaika technique called "artificial harmonics." The only "natural" harmonics you can reliably get on a balalaika are octaves and fifths above the open string – others exist, just like on any length of taut string, but they're hard to coax out. Not to be deterred from playing entire melodies on harmonics, enterprising balalaechniki came up with an alternative wherein instead of using your left hand to divide the open string into the proper ratio and your right hand to pluck, you finger any ordinary note with your left hand, touch the string at the octave of that note with the index finger of your right hand, and pluck with your right thumb. Voila! Harmonics of any note you please! Maybe physics should be my favorite subject!