The Star Light amplification system or S.L.A.S. was first introduced in this episode. It appeared in two others: "Fallen Angel" (2nd season) and "Escape" (4th season).
This episode shows The F.I.R.M's headquarters for the first time.
In the opening scene in the Russian laboratory, the shots of the lab rat and monkey are actually from The Andromeda Strain (1971), inter-cut with new footage of the scientists and close ups of the chemical vials.
This episode marks the first usage of Archangel's real full name: Michael Coldsmith Briggs III.
The song the Russian is singing in the kitchen is "Polyushko polye," a song written in 1933 as part of a Russian symphony called "A Poem about a Komsomol Soldier.". It is not, however, a song about bloodshed as Moses Rostoff claims. The song is not about battle, it is about a Red Army soldier leaving home to keep watch for his country's enemies. The title translates basically as "Oh Fields, My Fields."