Psuedolus - it obviously takes longer to read something that isn't there then it actually does to read something that is there. This is because the quantum flux of the probability and improbibility particles in the non-existant vibrate at a rate that is incompatible with both vision and electonic transmission of the information. However, you will be glad to know that all non-existant threads are archived in the Library of Unseen University in Ankh-Morpork; where for the mere bribe fee of a banana or two the Librarian will allow you to peruse them at your leisure.