If F(x) has a periodic attractor or exhibits chaos we refer to the Feature F(x) as a snag. The simple snag studied here has three straight line sections as for the trap above, but the central section has slope s where
This range for s ensures that the piecewise linear mapping remains within
the square feature box of side 
. The snag consists of a
self-contained chaotic attractor from which the motion cannot escape
unless there is added system noise.
Figure 2: Two of the possible Features.
If, on the other hand, the points (turning points) of the snag extend beyond the region of the Feature as in Figure 3 then the chaotic motion within the snag will occasionally escape onto the larger region where it will stay until recapture. This we term crisis-induced intermittency. When the points approach (from inside) the Feature box walls, arbitrarily small amounts of noise may contribute to this escape. Observation of the dynamics will not help to decide on the size of the snag compared to the size of the Feature unless the added noise is known accurately.
Figure 3: The mapping leading to crisis-induced intermittency.