A smallish nail set works wonders on those tight knots. The end is blunt so there's not much risk of damaging the cord, and they're forged and hardened to drive nails so they don't bend easily. I've gotten quite a few knots out of my HH spectra with a nail set, and I can't really imagine a worse cord to try and loosen.
"Physics is the only true science. All else is stamp collecting." - J. J. Thompson