Where would twisting waves be encountered (if you can’t see them in water)?
They appear in rigid systems, such as beams or bridges. The Tacoma Narrows bridge failed because of a torsional (twisting) motion of its deck, driven by the wind. Before it failed, it was carrying torsional waves back and forth along its length. Torsional waves also appear in less spectacular engineering situations. When you lean on a loose tabletop, you actually send a torsional wave through it. However, it’s so rigid that the wave is tiny and travels too quickly for you to see.