Doctor Who: 10 Secrets Of The Sonic Screwdriver You Need To Know

In Series 4's Silence in the Library, Donna asks the Tenth Doctor to use his sonic screwdriver on a door. He replies that he can't, because it's made of wood. Thus began the long-running gag that, for all its wonderous abilities, the trusty screwdriver simply doesn't do wood.

This joke ran throughout the entirety of Steven Moffat's time in charge, and has entered popular culture as one of the most well-known phrases in the show. The question is, why? Why doesn't it do wood?

Series 8 pitted the Twelfth Doctor and Clara against a giant forest that covered the Earth overnight. This, naturally, spells big trouble for the sonic. After scanning a nearby tree, the Doctor notes that they have "No circuits" and "No mechanism", and that "[The sonic] interacts with any form of communication you care to mention. Sadly, trees have no moving parts and don't communicate."

In other words, the sonic only works on machines, and not on anything organic. If there was a robot with wooden casing, then it would work fine, but pure wood on its own? No chance.

Maybe the Master should build an army of wooden monsters if they really want to come out on top.