Daniel states that trepanning was a common medieval practice and his reaction implies that it means almost certain death. Drilling holes in someone's skull to let the bad out was very common for a very long time in many cultures. Up to 10% of all stone age skulls discovered have evidence of trepanning and most of those show bone restructuring at the edges of the hole, meaning the patient lived long enough for the wound to heal. Think about that; in an age when the most advanced tool was a sharp rock, not only was trepanning common but it was commonly survived.
Before the credits, Daniel says, "That means that the Stargate is still in use by someone." and Jack responds by putting his pinky finger to the side of his lip à la Dr. Evil from Austin Powers: International Man of Mystery (1997) and saying, "Or some*thing.*"
The Canon recites a shortened version of the modern "St. Michael's Prayer." The full version is:
"Saint Michael the Archangel, defend us in battle.
Be our protection against the wickedness and snares of the devil;
May God rebuke him, we humbly pray;
And do thou, O Prince of the Heavenly Host, by the power of God,
thrust into hell Satan and all evil spirits who wander through the world for the ruin of souls.
Amen."