Blue stabiliser

The blue stabilizers were a component in the TARDIS which stabilized the TARDIS in flight and stopped it from shaking wildly. The Doctor stated that the blue stabilizers have no purpose, other being blue. River Song knew what they were, supposedly before the Doctor, and used them to stabilize the TARDIS. After the TARDIS stopped shaking, the Doctor nicknamed them "blue boreingers", and said he found the journey no longer fun. (DW: The Time of Angels)