Sirius and Reamus looked clueless, Snape sighed then spoke "The inaction is captis cogitationes however it is specifically a non verbal spell. You have to first think of the memory, while thinking of the spell and channeling your magic through the wand to catch it. You have think of the entire memory and then go blank. You must think of it without emotion otherwise it will get clouded, you must think of it and nothing else otherwise you will loose the string and corrupt the memory..."