What technique is used for the heads in this LEGO Halo Elite MOC?

Question

Just got back into LEGO after a decade, so I'm not familiar with some of the new bricks or techniques. I want to recreate some of the builds from the Silent Cartographer MOC but I can't figure out how.

(From a imgurl album:)

The elite heads have a 1x1 half circle and a 2x1 slope, neither have studs so they can't be attached to anything there since the rest is all upside-down. The 1x1 tooth is upside-down and attached to the 1x2 with 1 stud and 1x2 groove hinge. They should just slide off, unless they're glued on.

Answer 1

You're just confusing part 11477 "Slope, Curved 2 x 1 x 2/3" with part 24201 "Slope, Curved 2 x 1 x 2/3 Inverted".

They are really similar and have exactly the same curvature - but the former (and older) has stud holes on the non-curved part, whereas the later (and newer) has hollow studs.

As far as I can tell, those heads are built using the inverted slopes and a 180° SNOT technique (i.e. building "upside-down").

Also note that this model is most probably using part 15573 "1x2 jumper plate with bottom antistud" instead of part 3794b "1x2 jumper plate with bottom bar".