Blue stabiliser

The blue stabilisers were a component in the TARDIS which stabilised the TARDIS in flight and prevented it from shaking around. The Eleventh Doctor originally believed the blue stabilisers to have no purpose, other than being blue. River Song however, informed the Doctor that they were in fact stabilisers, and used them to stabilise the TARDIS. After the TARDIS stopped shaking, the Doctor irritatedly called them "blue boring-ers", and said the journey was no longer fun with them activated. (DW: The Time of Angels)