Evangeline Lilly makes her fourth of five appearances on Smallville as a non-speaking extra here. She had previously appeared in Kinetic, Visage, and Rosetta; she'll make her final appearance in "Delete". She can be seen in the opening movie theater scene, sitting behind Clark and Lana, wearing a bright yellow shirt.
The location that was scouted for the river scene, where Emily Dinsmore pushes Lana off a bridge and into a river, became problematic on the first day of shooting. The river had become too dangerous to shoot the water scenes, so they simply tied Kreuk to a safety line and had Jodelle Micah Ferland (Emily) push her over the edge, but without her actually going into the water. They moved the set to a sound stage where they filmed Kreuk's remaining scenes--where Tom Welling dives into the river to save her--in a water tank.
The article about Emily's drowning states that over the last 15 years before the incident, three more people drowned in the river. It also states that Emily saved Lana at the cost of her own life; something that isn't stated aloud in the episode until close to the end.
The movie that Pete, Clark, Lana, and Chloe are watching at the Talon is House on Haunted Hill from 1959.
Emily Dinsmore is the first known character, aside from Clark with super speed. Emily shares some 'Clark time' with Clark when they are both traveling at super speed.