This episode contains the first use of the word 'cloaked' to describe an invisible ship. All previous references to invisible ships have been 'stealth.'
When Archer and Reed are exploring the holographic device in Daniels' quarters, various future Federation starships can be seen, including the Defiant-class, Intrepid-class, Excelsior-class, and the Nova-class.
First appearance of Breezy the Beagle as Captain Archer's dog Porthos. In previous episodes, since the pilot, the beagle Porthos was played by Prada. However, Breezy had previously been used as a stand-in for Prada in some scenes in a few episodes, when a more "agressive" bit of dog acting was required. Prada is a male beagle, whereas Breezy is a female. The character Porthos is supposed to be male.
This is listed as one of the "Ten Essential Episodes of Enterprise" in the 2008 reference book "Star Trek 101" by Paula M. Block and Terry J. Erdmann.
With this episode, Enterprise is the first Star Trek series to end in a cliffhanger at the end of its first season.