- "Why does this always happen to me?!"
- ―Sylvester Siler after being electrocuted.[src]
He attempted to cut through the Virus Orb after it opened and one of the spikes pierced Colonel Jack O'Neill's shoulder. When he was about to cut through the orb reacted and moved the cut portion into the wall. (SG1: "Message in a Bottle")
When Stargate Command was dialed into P3W-451, he and Colonel Jack O'Neill attempted to shut down the power to the Stargate in the Stargate Command power vault. Unfortunately, the circuit breakers overloaded and he was severely burned. He recovered and aided Carter, O'Neill, Teal'c and Colonel Frank Cromwell detonate a shaped charge to cause the wormhole to jump. (SG1: "A Matter of Time")
When Major Samantha Carter and Teal'c along with two other SG team members were trapped on P9Q-281, he worked on solving the problem with the Dial Home Device but was unsuccessful. After O'Neill figured out a solution, he was given the Power booster device to study by Dr. Daniel Jackson. (SG1: "The Fifth Race")
When SG-1 found a crystal skull on the planet P7X-377 and Dr. Daniel Jackson disappeared, he and Dr. Robert Rothman were assigned to study it but could not determine its function. (SG1: "Crystal Skull")
When SG-1 beamed the Alpha Gate to the Biliskner, he supervised the installation of the Beta Gate at Stargate Command. He then traveled to the Naval base where the Blackbird was docked and helped to coordinate the destruction of the Replicators. (SG1: "Small Victories")
When Colonel Jack O'Neill had the Atanik armband on and patted Siler on the shoulder, the sheer force pushed Siler off a ledge. He sustained a broken arm and concussion in the process which resulted in O'Neill, Samantha Carter and Daniel Jackson being put under guard. (SG1: "Upgrades")
When SG-1 went missing and NID Colonel Frank Simmons took over the SGC, he helped Major General George S. Hammond and Harold Maybourne to surreptitiously enter Stargate Command and travel to Chulak without Simmons being the wiser. (SG1: Survival of the Fittest)
He was assisting Major Samantha Carter overhauling the Stargate's capacitors when they overloaded. He suffered a burn on his hand and Carter was knocked unconscious but quickly recovered. (SG1: "Prophecy")
In the final version of the simulation Teal'c got trapped in by the virtual reality pod, Siler was a Goa'uld infiltrator. After Siler was revealed as the infiltrator, he was killed by Teal'c with an FN P90 Personal Defense Weapon, ending the simulation. (SG1: "Avatar")
When the Replicators invaded Stargate Command, he was trapped on Level 8 and was freed by Brigadier General Jack O'Neill and Colonel Albert Reynolds. They held the Replicators at bay while he attempted to dial the Alpha Site. He was unable to do so because of an incoming wormhole from Dakara that destroyed the Replicators. (SG1: "Reckoning, Part 2")
Siler sometimes helps Samantha Carter work on her motorcycle. He has a set of pajamas given to him by Jack O'Neill. In 2004, O'Neill said that his collection of The Simpsons video cassettes will go to Siler. One year later, he learned that he was in Siler's will. (SG1: "The Curse", "Lost City, Part 2", "Reckoning, Part 2")
- Because of Shea's lisp, the writers would often give him lines with a hard S, such as "Sorry Sir". Dan Shea would say it as "Thorry Thir"; which would also explain both his first and last name. However in season 4, his name was Dan Siler.
- Siler has a tendency to be the victim of electrical shocks because of his work with the high-powered Stargate, though none of these have been life-threatening so far. As a running gag, he is often injured, either by the electrical systems, enemies, alien devices, his own wrench (the one needed for the capacitors of the Stargate), or "tests." After an incident in "200" in which the Stargate malfunctions and an electric shock hurls him across the room, Siler mutters, "Why does this always happen to me?!" (albeit this was a story fabricated by Martin Lloyd). Once he even walked head-on into a door that he had not noticed due to being distracted by a passing Sam Carter and Vala Mal Doran who had returned to base while both stunningly dressed up from a night of shopping.
- Along with Jack O'Neill, Daniel Jackson, Samantha Carter, Teal'c, George S. Hammond and Walter Harriman, he is one of only seven characters to appear in all ten seasons of Stargate SG-1. Of these, Siler is the only one who did not appear in "Children of the Gods".