When you're working in an agile pair and have control of the keyboard (known as "driving"), remember that your pair is almost always reading something on the screen, and it might not be the same thing that you're looking at.
While you're editing some code to make a test pass your pair might be looking at different code in another window, thinking about your next steps.
If you've got multiple windows open (code in an editor, tests running in a terminal or a web page in a browser) try and make sure that the windows don't overlap. The chances that they're reading something when you hit Alt-Tab are high, and there's no need to stop their thoughts in their tracks just because you've switched to a different window.
I normally go as far as to arrange the windows on my desktop in a consistent manner when pairing, so that both members of the pair become habituated with which terminal to look in for test output, etc.