This is one of these tricks that is almost impossible to knows except by coincidence, so perhaps some of you would benefit from knowing of its existence to apply it in certain situations.
Performing the trick is really simple: you just have to open an animated GIF as the one from this link and press and hold pause to stop the animation, while if you release it, the animation will return to normal.
For those of us who usually see funny GIFs on the net, it may be useful from time to time, and if it is not, nothing happens, you already know that knowledge does not take place.
Source | OSXHints