On how to tie tzitzit (another one of those very "visual" descriptions in words). Including the winding and knot-tying of the 8 threads on the corner. Also, the interaction of colors of blue and white, and which is considered holier - for an increasing level of holiness in how they are tied, with symbolism and deeper meaning as implied. Plus, how wool strings will cover the mitzvah of tzitzit for a 4-cornered garment made of linen, without a concern of sha'atnez (the reverse may not be an issue of sha'atnez either, but it's more complicated - and doesn't work - because of the blue string needing to be wool). And what about silk?