Probably by trying to do something like Ctrl+Alt+F1, or Ctrl+Alt+Backspace, or similar stuff, and hitting the wrong key. Or, by holding Ctrl+Alt and trying out

Probably by trying to do something like Ctrl+Alt+F1, or Ctrl+Alt+Backspace, or similar stuff, and hitting the wrong key. Or, by holding Ctrl+Alt and trying out all keys, out of pure curiosity.