Group phenomena have been used since antiquity in therapeutic, social, economic and political domains. According to Bion, the interactions between group members generate a "group unconscious" and its behavior is governed and oriented by Bion's "basic assumptions." The present work has been conducted during group analysis training at the Basque Foundation for the Investigation of Mental Health (OMIE) at Bilbao, consisting of eleven sessions. The participants are presented with an "absurd questionnaire" proposing 50 pairs of images, in each of which one image has to be chosen. The results are used to search for evidence in favor of the influence of group dynamics on individual choices of the images proposed in the questionnaire. Our analysis finds some evidence for an effect of group dynamics both on the initial choice of the pictures and on the evolution of the number of changes (swaps) of picture choices across the eleven sessions. We interpret these effects in the light of Bion's view of group dynamics, which postulates an immediate onset of the unconscious and its evolution during the group activity.