A compulsion is anything you do to reduce the distress an obsession causes, or to prevent the feared outcome. Nothing in that definition requires it to be visible. An enormous proportion of OCD is conducted entirely inside someone’s head, which is why so many people go a decade without diagnosis, and why so many courses of ERP silently fail.
What they look like
Reviewing. Going back over an event to establish what happened, what you said, how you reacted, whether your face did something incriminating.
Checking a memory. The same as checking a lock, performed on the past. Did I really? Was I definitely? What did I feel at that moment?
Mental arguing. Constructing the counter-case. Listing the evidence that you would never, that you aren’t, that it didn’t happen. Immensely reassuring for four minutes.
Neutralising. Replacing a bad thought with a good one, a bad image with a safe one, saying a phrase in your head, undoing.
Counting, repeating, praying. Silent versions of the same rules that govern the visible rituals — until it feels right, in the correct order, without a bad thought intruding.
Self-monitoring. Checking your own arousal, your own reaction, your own feeling toward someone, to see whether it’s the right one. Central in relationship and identity themes.
Mental confessing and reassuring. Silently telling yourself that you would tell someone, or rehearsing how you would explain yourself.
Why they’re harder than visible ones
Three reasons. They’re always available — you can’t leave your own head, so there’s no equivalent of moving the hand sanitiser out of reach. They’re invisible to everyone including, often, you. And they do not feel like rituals; they feel like thinking, and thinking feels responsible.
This last point is why rumination is the compulsion people fight hardest to keep.
Rumination isn’t an obsession
A distinction that changes treatment. The obsession is the intrusive thought — unwanted, unbidden, arriving on its own. The rumination is what you do next: the deliberate mental work of trying to resolve it. One is involuntary. The other, uncomfortably, is a choice, and it’s the half that ERP targets.
People resist this hard, because it doesn’t feel like a choice. The useful test: could you, in principle, notice you were doing it and deliberately not continue, the way you could take your hand off a tap? For rumination the answer is yes, with practice. For the intrusive thought itself, no.
How ERP handles them
Response prevention applies to internal acts exactly as it does to external ones. In an exposure, you approach the trigger and then don’t neutralise, don’t review, don’t construct the counter-argument, don’t check how you feel about it.
Clinicians use several tools for this: scripts you listen to on a loop, so there’s no room to argue back; deliberately holding the uncertainty in mind; and noticing-and-returning, where you catch yourself ruminating and drop it mid-sentence without finishing the thought.
Which is why a clinician’s answer to “how do you handle mental compulsions?” is the most diagnostic screening question there is. An exposure programme that doesn’t find these will produce weeks of distress and no improvement, and both of you will conclude that ERP doesn’t work for you.