Recently, many philosophers and psychologists have claimed that the explanation that grounds both passivity phenomena in the cognitive domain and passivity phenomena that occur with respect to overt actions is, along broad lines, the same. Furthermore, they claim that the best account we have of such phenomena in both scenarios is the "comparator" account. However, there are reasons to doubt whether the comparator model can be exported from the realm of overt actions to the cognitive domain in general. There is a lingering worry concerning such explanations of thought insertion: the "What is compared to what?" problem. Here I examine two ways to tackle this problem. First: thought insertion consists of the misattribution of strings of inner speech which are not attenuated (thought insertion is thus another name for auditory verbal hallucinations). Second: thought insertion is misattributed inner speech which exhibits the same phenomenological characteristics as normal inner speech. After explaining the types of problem that each of these potential solutions faces, I conclude with a set of open questions that the comparator theorist has to tackle.