Wait for the entire screen to load with all four horses and a fence in front of them. Then click on each horse.
Make sure your sound is on.
Reclick on any horse to make it turn off or turn it back on again.
http://svt.se/hogafflahage/hogafflaHage_site/Kor/hestekor.swf
Try clicking on the horses from left to right then right to left then just one or two at a time. It's fun and a good stress reliever.
You might find, however, that if you get them all going at the same time, it is too exciting. If this is the case, you can always click on one or several of them to dull them down.
Have fun!