After Fezzik dunks Inigo into the barrels of water to sober him up, every time they put Inigo on the screen during his conversation with Fezzik, Inigo's hair is different.
It is like they filmed it maybe 3 separate times and spliced it together so that every time they panned back to Inigo it came from a different "take" and therefore his wet hair looked different. It goes like this through the whole conversation with Fezzik. Once noticed it becomes very apparent and can be distracting to watch.