"Propeller blade" districts are districts which have two sections joined by only a single point. Such districts have been held in some courts to be contiguous.
For a good example (unfortunately neither county names nor district numbers are displayed), look at this map of the North Carolina House districts just imposed by Judge Jenkins:
See that bright green district in the south-central part of the state? It includes all of Richmond County, and about half of Stanly County, and the two are joined literally by a single point. Moreover, that single point (the hub of the propeller, so to speak) joins the two parts of that purpleish district; Montgomery County on the north, and Anson County plus part of Union County on the south. Thus, there are two "propeller districts" intersecting at a point.
Now, you might argue that it's physically impossible for both districts to occupy that single point where Stanly, Montgomery, Richmond, and Anson Counties come together. I sure would, and do. But some court, somewhere, decided that such an arrangement constituted contiguousness for both districts. That's inconsistent with my understanding of physics (two objects occupying the same place at the same time, and all that), but inexplicably, they didn't consult me.
As a side note, in this particular case, the point where the two districts cross each other is in the middle of the Pee Dee River, miles from the nearest bridge. So if either of the two State Representatives wishes to traverse his district, he must pass through the other district to do so.