This paper provides new data on the shiftiness of knowledge utterances (the phenomenon by which our inclination to ascribe knowledge shifts with the mentioning of non-epistemic factors). We confirm two hypotheses. The first one is that people's inclination to ascribe knowledge correlates highly with their feeling of confidence in the target proposition. The second one is that the shiftiness of knowledge utterances exists only in cases in which the assessor of the knowledge utterance does not feel certain about the target proposition. These results provide support for a certainty condition on assessments of knowledge utterances, as well as some pressure on some of the existing theories of the shiftiness of knowledge utterances, like semantic contextualism or various forms of sensitivism.