Untying tight wind knots

Wind knots - which have nothing to do with wind by the way - often seem to tighten up more than any manually tied knot.

These knots not only weaken the leader but also seem to have an ability to pick up any small piece of weed or get even more tangled for each cast.
Better untie them!

But... how do you untie a tight knot on on a 4X tippet? Nails and teeth are usually no good on these thin lines and small knots.

You use a fly!

Fly hooks have extremely sharp points and will enter even the most minute hole between two strands of mono and force them apart.
Take a closer look at the knot and find the largest arc of line on its outside. Gently press the hook point in between it and any neighboring line. The pressure alone will mostly open the knot a bit. Keep on pressing until the hook is all through. Watch out for your fingers!

The knot is now a bit looser. Use the hook or your nails to grab any open arc and pull. In most cases the knot will untie. But particularly tight ones might call for a second hook. Pass it down along the shaft of the first one and in between it and the line. Pull the two hooks apart and untie the knot.
Do not use hooks that a sharpened with edges or grooves. These will cut the line or at least mar it.

When the knot is undone, stretch the line and run it between your lips and test whether it is scratched or nicked. If that is the case your work unfortunately was in vain! Cut off the ruined part and replace it.