One of the arguments for active externalism (also known as the 'extended mind thesis') is that if a process counts as cognitive when it is performed in the head, it should also count as cognitive when it is performed in the world. Consequently, mind extends into the world. I argue for a corollary: We sometimes perform actions in our heads that we usually perform in the world, so that the world leaks into the mind. I call this internalism'. Internalism has epistemological implications: if a process gives us an empirical discovery when it is performed in the world it will also give us an empirical discovery when it is performed in the head. I look at a simple example that highlights this implication. I then explore the relationship between internalism and active externalism in more detail and conclude by comparing internalism with mental modelling.'