The Manchurian Candidate 2004 question (spoilers)

I recently watched it for the first time. In one scene Denzel bites the implant out of Raymond Shaw’s shoulder. Yet Shaw still obeys his trigger phrase and takes on his final mission. What was the implant for, just tracking? It also seems like Shaw’s doctor must not have been very thorough in his exams to miss a lump on the surface.

Didn’t they get to Shaw with a brain implant?

~Max