Gherkin Vacuum Motor

Four gherkins are briefly heated in boiling water, pierced with a nail, then attached to a horizontal cross and placed in a bell jar. The air is pumped out the jar and the gherkin construction begins to spin.

How does it work?
Gherkins are mostly made up of water. When the pressure in the bell jar is low enough, the water becomes gaseous and escapes through the hole made by the nail. The escaping water vapour creates a recoil which causes the cross to spin.