Cold welding is the phenomenon of two pieces of metal fusing on contact. It's a big problem in space, but it can even happen on earth at room temperatures with the right metal, as Cody demonstrates.
Bonus video: cold welding gold:
Bonus bonus video: for more on the problem in space, this explainer gives details and ways to avoid the problem if you plan a space trip sometime soon.
• Cold Welding in Atmosphere (vacuum tests to come) (YouTube / Cody'sLab)