Continuity mistake: When Hoshi returns to the ship, Archer says in his log that Trip and Malcolm are taking her back to Enterprise. Trip wasn't on the planet: the landing party was Archer, T'Pol, Hoshi, and Malcolm. (00:11:20)
Continuity mistake: In the scene in T'Pol's quarters, after she and Tolaris have mind melded and she asked him to leave, he walks out, and the door starts to close before the shot changes to T'Pol. But when the shot changes, the light from the door on T'Pol shows the door still opening, and then closing. (00:33:40)
Terra Nova - S1-E6
Continuity mistake: The bike wheel is first shown spinning counterclockwise, as expected from the previous shot, but then it rotates clockwise in the next shot. (00:06:44)
Continuity mistake: Archer, T'Pol and Trip enter the cloaked Suliban ship, after Trip uses the stun grenade. Archer exits the docking bay first, followed by T'Pol and finally Trip, however in the next shot Archer and Trip are together and T'Pol exits for a second time. Also as she exits the door closes behind her, but in the following shot the door closes again. (00:28:00)
Answer: While ratings did drop, there was a lot going on to cause the rating drops and cancellation. First, "Enterprise" was on UPN, which was dissolved a year after the show was cancelled. At the time of cancellation, it was UPN's highest rated drama. Because they were on at night, they were often preempted by local UPN broadcast of baseball games. And it wasn't even aired in every market. They also lost a major corporate backer early and it was difficult for them to over come that loss. Plus, for season 4, they switched to a Friday night line up, so they were competing against Fox shows, like "The Simpsons" whereas on Wednesdays they didn't have much competition.
Bishop73