Understanding the notional machine that conceptually executes a program is a crucial step towards mastery of computer programming. In order to help students build a mental model of the notional machine, visible and tangible computing agents might be of great value, as they provide the student with a conceptual model of who or what is doing the actual work. In addition to programming, the concept of a notional machine is equally important when teaching algorithmic design, complexity theory, or computational thinking. We therefore propose to use a common computing agent as notional machine to not only introduce programming, but also discuss algorithms and their complexity.