> This works on people as well!

Only within certain conditions or thresholds that we're still figuring out. There are many cases where the more someone recalls and communicates their memory, the more details get corrupted.

> Cops do this when interrogating.

Sometimes that's not to "get sense of the variation" but to deliberately encourage a contradiction to pounce upon it. Ask me my own birthday enough times in enough ways and formats, and eventually I'll say something incorrect.

Care must also be taken to ensure that the questioner doesn't change the details, such as by encouraging (or sometimes forcing) the witness/suspect to imagine things which didn't happen.