Traditionally, to test whether the hypothesised organisation of behaviour generates the behavioural markers selected for measurement has required experiments or comparisons across species, sex and age. In the last couple of decades, important strides have been made in developing ways to create virtual animals, either on a computer screen or as freely moving robots, that can be programmed to produce the behaviour of interest. If the programmed rules are sufficient to produce the behaviour of real animals, then that adds independent evidence for the proposed organisation. Novel testing methods is one direction for the future. Another is to identify additional organisational principles. For example, some level of randomness seems essential for the production of effective functional behaviour. A challenge for the future is to understand how random processes are integrated with the causal processes described in the preceding chapters.