Is my jade Ghostface pendant going to snap at the mouth?

Jade is actually one of the tougher stones out there, so thin sections alone don't scare me much. The catch is that toughness only works when the stone is intact. A hairline fracture running across a thin jaw is the weak point, not the thinness itself, and that's the thing you need to figure out first.

The way I check lines like this is to shine a strong flashlight from behind the piece in a dark room. A natural inclusion or color banding will just show as texture in the green. A real fracture will light up bright and usually has a slight offset or a diffrent sheen to it. A jeweler's loupe helps too, since a crack will catch light differently than the surrounding polish. If the line is only visible from one angle and disappears when you tilt it, it might just be a grain line in the stone.

If it turns out to be a geniune hairline crack, a thin low-viscosity epoxy wicked into the fracture can work, but you're right to be cautious about cloudiness. On polished jade I've had better luck keeping the crack itself dry and instead handling it structurally. G2 super glue style thin CA glue is another option people use on carvings, it penetrates deep and dries pretty invisible on green stone, though it can leave a slight sheen change where it saturates the surface. For the bail, placement matters more than people think. Don't drill thru the jaw or anywhere near that fracture line. Drill into the solid mass at the top of the head, as far from the thin section as you can, and keep the hole shallow. A through-drilled bail chain setup puts less leverage on the carving than a glued cap does anyway.

Honest answer on wearability, if the crack lights up bright under the flashlight I wouldn't wear it as a daily pendant. Pendant life is hard, they knock into door frames and counter edges constantly. If it's just a faint grain line, jade will honestly shrug off knocks that would kill most other carved stones. Wear it gently and keep a jeweler's rogue and leather wheel handy for touch-ups later.

Agree with the drill placement advice big time. I carved a bat out of nephrite a couple years back and put the bail hole right at the top of the head instead of anywhere near the thin wing tips, and it's survived plenty of bumps since. One thing I learned the hard way though, go slow with the drill and use water, jade heats up fast and a heat crack looks alot like the fracture you're worried about. I still do the flashlight check before wearing mine out on Halloween nights, gives me peace of mind.

Way back when I was learning, the old guys I worked under always said a carving like that should have a heavier back side left in the design on purpose. Slim wispy parts were fine if there was a solid spine of stone behind them taking the load. Too late to change your design now, but it might explain why the jaw feels dicey to you. One thing I used to do with questionable lines was rub a little mineral oil on the surface and watch if it wicks in and darkens along the line. If it does, that tells you the crack is open to the surface. If it stays put, you probaly got lucky and it's just a grain seam.

I've never touched real stone, I mostly mess around with carving shells and the odd piece of tagua nut, but your post makes me want to try jade someday. Question for you though, how did you even get started on it? Did you begin with small practice chunks or just go for it on a good piece like I somehow always end up doing? I ask because the one time I tried working with a harder material I cracked it halfway through and had no clue if it was me or the material. Either way the screaming mouth sounds like a fun challenge, I'd love to see a photo when the bail is on.