They are fascinating to observe

Their personalities vary a lot so some may be more cheeky or communicative than others and some may depend on the level of bond. I've had hard stares, (let me out human), black looks (what have you done?! Shock horror), sulks (turning away and presenting the back end), guilt-tripping (sad eyes pleading looks). One of my Syrians kept tricking me into thinking I'd forgotten to put his veg out. I was in a routine, and thought I had put his veg out when I put his food out, but saw him sitting next to his veg plate looking at me, looking at the plate, looking at me - waiting. I thought - oh maybe I forgot to put the veg out (every day seemed the same), so I went and got a bit and put it on the plate. A few minutes later he was doing the same thing again! I just said oh no you're not fooling me this time - I know I put it out!
Sometimes looks and behaviour can be very communicative. Eg indicating there's a problem - water bottle or bowl empty (frantic to get your attention or going over and looking at it and looking back at you - literally pointing at it with their heads). Or wheel jammed - similar. So any frantic behaviour things should be checked out.
It's fasincating how intelligent and communicative they can be

Jealousy is another one. I have two Syrians - if I talk to one, the other sits staring at me jealously from the side of the cage. Dislike or particular like of certain humans! One of mine didn't like men.
Looking happy - yes they can look happy. Looking cheeky - twinkle in the eye and head turn. The guilt is the worst one!