Carl's new toe ring, which must be removed while he is unconscious for the memory treatment to work.
The treatment requires that someone remove Carl's new toe ring once he is knocked out, which is part of why the procedure has to happen in the Field Hospital independent of the safety of the guild rather than inside a saferoom. Carl asks whether the dive can even function with the ring off; Rosetta tells him that once he is under, the ring should not matter, and they will make sure it is back on his toe before he wakes up.
Imani's protection spell and Carl's fed Emberus shrine are meant to cover the gap the missing ring leaves in his defenses.
A ring worn on Carl's toe.
Protective item that must be stripped for the drug dive, creating a window of vulnerability.