This paper extends some previous work reported [1] at COMPLEX96 and developed [2] at the Circuits Conference ECCTD97 in Budapest, on simple electronic iterating circuits containing traps and snags. The present paper also relates that work to the behaviour of artificial network traffic models reported [3] at COMPLEX94 and in a paper [4] in the International Journal of Electronics where the mathematics is presented in full. These systems, together with a piecewise-linear dynamical system comprising a two-centre harmonic oscillator, are interpreted as examples of a Variable Structure System (VSS). New observations are reported, of VSS-induced blocking behaviour on networks and of the Crisis-induced intermittency which has been observed by direct experiment in the electronic circuits described [1] at COMPLEX96, and is presented here in detail for the first time.