E. Cobham Brewer 1810–1897. Dictionary of Phrase and Fable. 1898.
Judas Slits or Judas Holes.
The peep-holes in a prison-door, through which the guard looks into the cell to see if all is right; when not in use, the holes are covered up.
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“It was the faint click made by the cover of the ‘Judas’ as it falls back into the place over the slit where the eyes have been.”—The Century: Russian Political Prisons, February, 1888, p. 524.
