As they get closer, the flaming desert trees start exploding. It's not really that unusual, though, more similar to the way they might explode from the sap inside them being reduced to steam during a forest fire.

It's mildly dangerous but as long as they stay away from the trees it won't cause any harm.

But it quickly becomes clear the threat isn't the trees themselves.

They're just the warning system.

Now that they've both been detected dust kicks up in the distance. Something is upheaving the sand and racing towards them, like something is tunneling underground towards them at rapid speed.