After accidentally cat a tar or zip file or left out some pipe and echo the whole file of random string, on to the screen; it can mess up the font of the screen and result in missing of characters or blinking characters or ever the cursor is missing from the screen. No worries, just a 5 character will make your screen back to original display :
Just type :
and press enter. It might hang there for a few seconds then the usual prompt would come back. In case it does not, just press once enter key.