Click on a SIRDSlet button to (re-)start a SIRDSlet.
If the applet does not start, you need to add http://www.benibela.de/bin/games/sirdslets/sirdslet_page.html to the Exception Site List in the Java Control Panel (jcontrol).
You should also select the SIS/SIRD-image that creates the nicest stereogram for your eyes. Notice that the flickering is usually necessary to recognize movements in the stereogram.
You can also press enter to switch between stereogram and height map display, or press escape to open/close the menu .
For more information:
BeniBela online
Lewey's World Website