You give your leg a tug and it remains submerged. It looks like you might actually have to put some effort into this one, so you grab it with both arms and give it a mighty heave... only to have it give unexpectedly the moment you start to pull. Before you even understand what's happening you feel a jolt as your head hits the pavement, and everything goes dark.
When you wake up, the moon's still hanging high in the sky. You couldn't have been out for too long. You feel a sharp pain in the back of your head, but rubbing it, you find only a small bump. As you slowly open your eyes, you begin to look around, but stop almost immediately when you see what looks like a seamless navy blue beach ball sitting on your chest. You give it a gentle prod, and it jiggles like a ball of gelatin. Carefully, you push it off of your chest, and rather than rolling away when it hits the ground it just stays put right next to you while you bring yourself to your feet, brushing yourself off with your hands.
It's late, your head is pounding, and you're extremely tired, so you decide to make your way home. Taking a last glance at the conspicuous ball (and noting the even more conspicuous fact that the puddles from before seem to have mysteriously vanished), you start wandering back to your house. After you've made your way about halfway back, you think you hear a noise behind you, so you turn around. Right there behind you is the blue ball, less than twenty feet away and not moving. Experimentally, you take a step back. It rolls forward by just as much as you've walked, pushed by some invisible force. You step back again; it rolls again. You try moving faster, but it manages to easily keep pace, and when you stop it stops just as quickly, maintaining the exact same distance. No, that's not quite right... it's actually CLOSER now!
Looks like you might have to put off going home just a bit longer; you've got to shake this thing!