I've said this before...want I reeeeaaaallly want to see is a greenscreen scene where the Doctor and Clara are crossing a bridge like the one they used for the Great Machine on Epsilon 5 in B5. Clara remarks to the Doctor about the vastness of the interior, and he turns around and says something like "If you think that's cool, watch this.": He pulls out a coin and drops a coin into the chasm. We see it disappear. "What's so special about that?" asks Clara. "Wait for it..." He holds out his hand, and the coin falls into his hand from above." He smiles, and turns away and crosses the bridge.
Oh that would be brilliant!