Attitude verbs describe mental states of their subject in relation to a proposition codified by their clausal complement. In this paper, we describe the behavior of such verbs in Karitiana, a Tupian language spoken in Brazil. Recently, it has been noted in the literature that embedded clauses with nominal features seem to lead to a factive reading of these verbs. In Karitiana, all embedded clauses are nominalized since they lack many clausal features, and conversely exhibit nominal distribution and behavior. We propose a structure with an N head for embedded clauses in Karitiana, which accounts for their morphological behavior and also explains why these constructions behave as strong islands. Judgments of contradiction with attitude verbs of Karitiana were collected and the results show that they fall into two categories: one that obligatorily entails the truth of the embedded clause and another that favors it, but that does not require it obligatorily. This shows that nominalization of embedded clauses seems to be tied to the presence of factive entailments, but this alone is not a sufficient condition to force a factive reading of the matrix attitude verb.