"...That's not a bird."

As you watch it, its wings tuck in and it begins to dive. As it does, it grows larger. And larger. And larger.

"That's not a bird!" you snarl again, drawing your sword and looking for some kind of cover. You take just a few steps before a the sight of a looming shadow sends you instinctively to your knees. The air is sliced above you, and a veritable storm of dust and dirt kicks up in the thing's passing. You cough, shielding your eyes, and rise to your feet. You try to get a look at your attacker, but all you can see is a flash of massive grey wings before it's arcing up, up into sky.

It's coming around for another pass. You know it is, there's no way it's giving up that easily. Sure enough, it starts to flip around to dive at you again. You have seconds to think and decide what to do.