It's probably a mock grenade, for 'decoration' purposes, like the little Alien on the case. It wouldn't be very intelligent to have a live grenade lying around, wouldn't it? It would be particularly dangerous on one of those days your PC doesn't do anything right. Then, instead of flinging your mouse across the room, you could blow it to high heaven.
On topic: announcing that you have to delay the demo 3 days before it's release sucks. What was Crytek doing before then? Sleeping? If you have given an exact date, you should stick to it. Also, the delay isn't 1 day, or week, but a whole damned month!
soldier37, screw the NDA, and just post the videos please. Who cares what EA thinks. There are quite a few beta clips on YouTube, but most don't properly mention the hardware and settings, or have a FPS counter. If the demo was being released as planned, I wouldn't have cared about the vids, but now, waiting one whole month is just too much.