In all latent trait models there is an equation which describes the probabilistic outcome of the interaction of a person with a known ability and an item with a known difficulty. This modeled outcome can be compared to the observed outcome, and the residuals can be summed over the items to assess the fit of the person to the model. Various approaches to this "person fit" analysis are explored, and the mathematics of person fit analysis with the Rasch model is briefly discussed. Various patterns of responses which seem to provide meaningful information about the individuals taking the test are reviewed. They include guessing, startup (fumbling), plodding, content interaction, sloppiness (carelessness), reanalysis, and random responses. Data from a specific algebra test are used to illustrate the extent that these patterns actually occur. (Author/BW)