This study aims to make a clear distinction between the processes of entrainment, detrainment, and mixing in cumuli. To this end, numerical simulations of three types of thermals are performed: 1) a dry thermal rising through a neutral atmosphere, 2) a dry thermal rising through stably stratified atmosphere, and 3) a dry through a conditionally unstable atmosphere. Numerical tracers, closed streamlines, and Lagrangian particle trajectories are then used to provide qualitative and quantitative pictures of entrainment, detrainment, and mixing in each thermal. These pictures provide some explanation for the observed evolution of mass flux profiles in shallow cumuli. They also suggest that simple cloud models used in convective parameterization schemes are missing an important aspect of reality.