Here are the slides of another talk I'll on networks I'll be giving at Oxford:
* [Network theory II: stochastic Petri nets, chemical reaction networks and Feynman diagrams](http://math.ucr.edu/home/baez/networks_oxford/networks_stochastic.pdf).
This is an intro to the stochastic Petri net stuff I've been banging on about for years. It should be self-contained if you read enough of the [overview talk](http://math.ucr.edu/home/baez/networks_oxford/networks_overview.pdf) to be unafraid of the phrase "symmetric monoidal category" (or if you just ignore it).
As usual, I really welcome comments, corrections, questions and complaints!