I've never seen it, but of course I have felt it sloshing inside a
fire extinguisher. I do introduce that phenomenon to my students in
what I consider to be a safer way. I also fire the CO2 extinguisher
over the heads of the students allowing them to observe the small
bits of frost that form on the particles of dry ice that condense
in the throttled CO2 plume.
For the triple point I use nitrogen. How many of you have seen
solid nitrogen? More than a thousand of my students have.