Doctor Who: 14 Cool Details In Steven Moffat & David Tennant's Silence In The Library Commentary
13. Tennant Disagreed With The Power Of The Sonic Screwdriver
Just after the title sequence, the Doctor and Donna have a nosy around the library, and the Doctor excitedly proclaims that they're in the biographies section.
Almost straight away though, the Doctor realises that something is wrong: they're standing in the biggest library in the universe... so why does it seem to be abandoned?
To find out what's going on, the Doctor heads to a nearby control station and zaps it with his sonic screwdriver, which reveals that there are over a million million life forms somewhere on the planet - which we later learn is due to a Vashta Nerada infestation.
Originally though, the Doctor didn't use a control station at all - he simply aimed his sonic into the air, and took a reading of the whole planet.
However, Tennant felt like this was a bit of a stretch - even by Doctor Who standards - and the scene was reworked into the version we know today.