Mental review is essentially a form of mental checking. It is the activity of looking at the obsessive thought/feeling/urge/etc and believing that you will somehow be able to solve or dissolve the obsession by thinking through it.
For example, if someone has the thought that they accidentally ran over someone with their car on the way home, they may replay the drive home over and over in their mind trying to convince themselves that nothing terrible happened. At some point, the process becomes so mentally taxing that they may begin to imagine that they did hit someone. Even though a person may not have hit someone in reality, repeatedly reviewing the situation leads to emotional and mental confusion, and ultimately leads to greater uncertainty. Unfortunately this results in doubt increasing as one continues to lose touch with the actual experience.
Therefore, even though the act of reviewing is internal and invisible to others, it is still considered a compulsive behavior that needs to be addressed to make progress in living with OCD.
When you’re engaging in mental review, the brain thinks there is more to discover. With mindful Exposure and Response Prevention, you expose yourself to the feared thought and teach yourself to have a different response. You are creating new neurobiology, teaching the brain to recalculate the significance of the obsession. Mental review may feel automatic at times, but with an increase of your awareness of your OCDs tendency to check, you can learn how to use the urge to check as opportunities to resist checking. Next time, you may not be as easily convinced to jump into mental review. You got this!