Phylogenetics has a central role in the biological sciences. We suggest a hands-on exercise to demonstrate the task of character coding and its importance in phylogenetic systematics. This exercise is appropriate for undergraduate students in life sciences and related courses. The teacher must provide a single group of masks in which color patterns, textures, and formats provide the characters to fill the data matrix. (The mask could be replaced by a set of other complex objects.) In this case, because there is no actual phylogeny, students will not be concerned with recovering the correct topology. Character coding is the aim of the exercise. After the character matrix is completed, a phylogenetic tree is drawn and the students interpret the evolution of a single character, starting from the common ancestor, based on the topological pattern of the tree and on the data matrix. In sequence, the students name and provide a full diagnosis for the group of masks as revealed by the topological pattern. The comparison between group results is also educational: there will be some common patterns between trees, but others will differ as in biological systematics.