Lest I be guilty of over-reliance upon the paperback writer's cheap expedient of suspense to keep you reading, I will reveal right now that they are vortex generators. Their purpose is to flush low-energy air out of the intersections. They do this by generating a tip vortex, just as any wing at a non-zero angle of attack would. The vortex, if you could see it, would look like a slender rope trailing from the vortex generator and following the contour of the intersection. In fact, when atmospheric conditions are right you can sometimes see just such vortices, made visible by condensation, trailing from vortex generators on the nacelles of some airline jets such as big-engine 737s. They appear at the same time solid and ghostly, and are capable of the most delicate, graceful and agile responses to changes in attitude or G-loading. They are, in fact, quite beautiful. In aerodynamics, aesthetic enjoyment is a frequent, albeit unintended, side effect.