[servo1969]

What sorcery is this?

Any ideas?

[servo1969]

Sir Bedevere: ...and that, my liege, is how we know the Earth to be banana shaped.
King Arthur: This new learning amazes me, Sir Bedevere. Explain again how sheep's bladders may be employed to prevent earthquakes.

[PastorBooks]

My blood does that all the time.

[Ray76]

triple point?

[FredZarguna]

Gonna guess it’s at the triple point, and solid, liquid and vapor are in equilibrium under the substance’s own vapor pressure. When the vapor is evacuated by the vacuum pump the decrease in pressure temporarily takes us off the TP, which causes some of the solid to liquefy, and some of the liquid to vaporize, restoring equilibrium.

[Darksheare]

Vapor pressure, without air pressure the fluid begins to undergo sublimation and bubbles.
Without air, the temperature drops rapidly and it freezes.

And then the videographer gets turned into a newt!

[MetaThought]

I guess the fluid has a fairly high freezing point when pressure is low. So evaporating liquid carries away heat, cooling the rest of the sample. Might be similar to the Mpemba effect

[HiTech RedNeck]

Formic acid would show a triple point at about 8 degrees C under a fairly good vacuum. I’m sure there are other organic compounds which would be even easier to manage.

[Vendome]

Sounds a good many women I know...

[Pecos]

It could be explained by time-lapse photography with unknown pressure and temperature changes using any number of fluids. Notice that you do not see any “outside” reference movement that you would recognize, such as a human being.

[BuffaloJack]

Believe it of not, I’ve actually done this boil/freeze thing.
I needed to fill capillary tubes with water and the capillary tubes were so small the water couldn’t overcome the surface tension to enter the tube. We put the tubes in a container of water, drew a vacuum and the water filled the tubes while boiling. This was delicate because the instant the water froze, from heat of vaporization loss, the tubes would break because the water would expand. We wound up using a 5 or 6 percent alcohol mix that kept the freezing from occurring.

[thackney]

Critical point
http://en.wikipedia.org/wiki/Critical_point_(thermodynamics)

[JRios1968]