Dr. Jones was terrified to find he wasn't riding alone. The legend of the desert ghost rider appeared to be true.
I had an elaborate rigging to make the skeleton horse & rider hover eerily behind Indy. This was probably the best frame of all shot and it happened to have the sand in just the right place to hide the rig almost completely, there's still a tiny bit of it visible if you know where to look. No photoshopping needed, though, which is always nice.