I am using Ubuntu 12.10.
See this short video of what actually shows up on screen when we successively press the Ctrl key twice:
https://www.youtube.com/watch?v=FFZTnNH5nIs
What does it do? Is it a shortcut? Acts as a Hotkey? A easter egg? What exactly does happen?
Now, once it has been activated, every single press of Ctrl key triggers this action.
That's just the "show mouse" highlight.
Settings -> Mouse and Touchpad -> Show position of pointer when the Control key is pressed.