Sandstorm often closes her eyes when i pet her head gently. I'm not sure whether she wants me to stop doing that or not, so i usually just stop so i don't overthink. Sometimes she only closes it for a second, and she doesn't seem angry, and tolerates everything. (not puffing out her beard or anything) Sometimes she also closes her eyes near her cage randomly when nothing seems to be bothering her. :?:
Sometimes it can mean relaxing. Sometimes it can mean mild irritation, but not enough to move or do anything about it. It's one of those things you'll need to interpret on an individual basis (this gets easier over time).