This work presents a methodology used to collect some spontaneous social affect corpus and preliminary prosodic analysis of certainty and uncertainty in Brazilian Portuguese. The corpus was collected by a Wizard of Oz (Emoz)method, the scenario to induce certainty and uncertainty is based on the situation of a job interview, for which a companion robot (Emox) is supposed to be a trainer. The subjects were convinced to benefit of a free training of this “revolutionary” method to train to job interview. In this scenario the linguistic expressions are partially controlled, in order to focus the certainty/uncertainty expression mainly on paraphrasing and prosody. Data were preliminary analyzed for audiovisual prosody: videos analysis were made regarding eyes, mouth and face/head movements, while audio analysis were made about acoustic prosody parameters of fundamental frequency and duration. The first results show that using Emoz within such a scenario is an efficient way to induct spontaneous but comparable speech production. Prosodic results show that fundamental frequency and duration measurements, as well as eyes, mouth and face/head movements, are differently used in certainty and in uncertainty production in Brazilian Portuguese.