Kenny Macfadyen, who is an expert on Scottish castles and is currently making a detailed map of the castle's walls, pointed to something which I can see but would never have thought about. Look closely at the two 'windows' at the level of the scaffolding boards.
It's the slate that interests Kenny. Even today, when we can import cheap slate from places like China and Spain, it's expensive stuff. At the time this wall was built, it would have been very expensive indeed. So why, with tons of stone readily available around the castle, was this precious material used to build this part of the wall?
Kenny makes the suggestion that, during one of Mingary's sieges, this part of the battlement was severely damaged. It had to be rebuilt while the siege continued. Since they couldn't go outside the castle to collect stone, the defenders, in desperation, tore the slates off the roof of the north range, easily accessible from here, and used them to rebuild their defences.
Many thanks to Kenny Macfadyen.