Do not just bring up the system and use it as the only prop. Explain the context in which it is used. Describe the next steps and how they will be accomplished. Present a compelling scenario. His point was that without a good example, no matter how good the rest of the work, the thesis wouldn't have a backbone.
Demos are like that.
For example, in Project Leap, which deals with process improvement, one good scenario might illustrate how a user collects data, interprets it, determines a potential improvement, implements it, takes more data, and interprets it to determine if improvement actually occurred. You might show a few slides, then a bit of the system, then back to the slides, then back to the system, and so forth. The immaturity of your research is no excuse for an unpolished demo. I have learned over the years that there is no relationship between the maturity of a research project and the quality level of the demo. Many excellent researchers use demos as one of their two primary mechanisms for pushing their research along.