Where is the "meta" in animal metacognition?

Apes, dolphins, and some monkeys seem to have metacognitive abilities: They can accurately evaluate the likelihood that their response in cognitive task was (or will be) correct. These certainty judgments are seen as significant because they imply that animals can evaluate internal cognitive states, which may entail meaningful self-reflection. But little research has investigated what is being reflected upon: Researchers have assumed that when animals make metacognitive judgments they evaluate internal memory strength. Yet decades of research have demonstrated that humans cannot directly evaluate internal memory strength. Instead, they make certainty judgments by drawing inferences from cues they can evaluate, such as familiarity and ease of processing. It seems likely that animals do the same, but this hypothesis has not been tested. I suggest two strategies for investigating the internal cues that underlie animal metacognitive judgments. It is possible that animals, like humans, are capable of making certainty judgments based on internal cues without awareness or meaningful self-reflection.