But I think this is supposed to be like. A much bigger and scarier scratching than a little thing like that'd make.

[Honestly, he is doing this mainly for the very enjoyable benefit of scaring the fuck out of Alphonse. He tilts his head back to glance more in his half-brother's direction, grin wiiiidening.]

I can't shut up, or we'll never find out what happens!

Also, how would you know? This tunnel is probably getting bigger and full of more tunnels all the time, it probably hasn't been explored all the way.