Is there a way to hide what you do?

We all know that on our walls facebook summarizes our latest activities ( like: XXX XXXX posted "hey Yo!" on YYY YYYY's wall"). When I go to some of my friends' walls I cannot see those things, even if they do it with friends in common. I've looked through the privacy settings for a setting to hide just that (since everything else is visible) but I don't see it

They've most likely hit the X button (while hovering one of those activities) and chose the "Hide all comment activity..." option on their walls. You can do the same.

Thanks