I'm kind of stuck inside the ride, and it seems a couple of my items have gone missing. For one, when I got Digger's attention with the spanner/wrench. If I take it to him, then give it back, Gromit will shake his head, and then, strangely, the spanner will be absent from my inventory. A similar thing happened with the red balloon I grabbed from the town square earlier, and I might have used it on the open grate at the top of the inflatable head, but it's gone missing from my inventory--and I was planning on using it, too.
Edit: The balloon disappears when you advance to the inside of the Muzzler. It might be automatic, but it does make me wonder if it has any use.