The iris is stated to be three microns in front of the gate's event horizon. For a sense of scale an average human hair is about 40 microns in diameter, a high grade cashmere fiber is maybe 15 microns. But a single atom is only about 1/2000th of a micron.
There is a scene in which Kawalsky is given a medical scan with his head inside a large ring device - approximately 6ft x 6ft x 2ft. This device is a real medical tomographic device manufactured in the early 1990s in Knoxville, Tennessee, USA. It is a PET (positron emission tomography) medical imaging device - likely a model 953. As the radioisotope in the device undergoes positron emission decay (also known as positive beta decay), it emits a positron, an antiparticle of the electron with opposite charge. Such equipment can actually show unusual biological activity in the body as a 3D volume image. At the same time, the 3D medical images in the next scene showing the parasite wrapped around Kawalsky's neck vertebra are at least partly made-up computer graphics.
When Captain Carter (Amanda Tapping) is slammed against the elevator wall, she hit her head on the wall and got a concussion.
Richard Dean Anderson (Colonel Jack O'Neill) previously appeared in an episode of MacGyver (1985) with the same title: The Enemy Within (1986).
This is the first Stargate production where the plot does not involve traveling to Abydos.