Inactive, it looks like an ordinary knife, but when its vibrating crystalline edge is activated, it can shear through almost any material short of military-grade vehicle armor.
Naturally, you have to remember to switch it off before trying to sheath it!
The other drawback of the weapon is the tell-tale blue glow that highlights the activated edge. This immediately tells any onlooker that you are handling no ordinary knife. If you haven't already given the game away, of course, by your ability to behead an opponent with a casual flick of a wrist.
Shimmerblades come in all shapes and sizes. Shayla favors a pocket knife. Small, innocuous, the sort of thing anyone might carry.
In the The Ashes of Home, Shayla is attacked by another assassin wielding a rapier shimmerblade. This confrontation highlights another limitation of the weapon: when two active blades clash, the results are unpredictable and potentially lethal to the owners. At best, the blades rebound with a ferocious, bone-jarring wrench. At worst, one or both blades could shatter, filling the air with a supersonic hail of needle-fine shrapnel.
These are not weapons you will ever see used in a swordfight.