On VT240 terminals, the keys Ctrl-s and Ctrl-q will not work properly in
Emacs.  Instead, you should use Ctrl-~ (for Ctrl-s) and Ctrl-\ (for Ctrl-q).

When you start Emacs on a VT240 terminal, you will see a warning message to
remind you of these changes.

If you accidentally type Ctrl-s on a VT240, your screen may appear to
"freeze".  Typing Ctrl-q should get you out of this situation.