Swamped

You don't think you can reach the reins from here. But you might be able to reach the desert-horse's hump.
You pull yourself down from the seat, trying to hold on as best as you can with just your legs, and reach out to the hump. Then you pull back as hard as you can.

Thankfully, the desert-horse seems to understand the signal, and slows to a stop. That gives Rider time to catch up, and help you down from your awkward position.

Up ahead, you see your assailant, sprawled on the ground. Rider wastes no time in rushing over and picking them up from the sand.

You can see now that it's a grebling wearing a bird mask and a cloak. Rider doesn't strain himself carrying them at all.

"Marshall," he says. "Do you notice anything odd about this mask?"

Why is he asking you? You're not an expert on bird masks.

Wait, but you do have ether senses. And you think they're acting up as you look at the mask.

But what could they be trying to tell you?