That's interesting. My PT noticed a dark spot on my scar (this was at about 4 weeks) and said he thought it was an undissolved stitch. I peered at it with a magnifying glass and decided he was right, so I pulled it out with a tweezers. Turned out it was about 1/4" long and the bottom was dissolved; the top part that was sticking out had not dissolved. But I didn't have any pain, and am surprised to hear that a stitch can be internal and undissolved.