Anti-dreaming device

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Tegan used the anti-dreaming device to protect herself from the Mara. (DW: Snakedance)

The anti-dreaming device was a contraption devised by the Fifth Doctor that, when worn, cancelled out the brainwaves associated with dreaming. The Doctor had Tegan wear it to stop her dreaming of the Mara. (DW: Snakedance)