I enabled Cloudtrail to log all DynamoDB read/write data events when trying to troubleshoot an issue. Even though I only left this enabled for a few days, the Cloudtrail line item was $5k more than it should have been. My back of the napkin math with assumptions came out to be 100 times less than that, so I had a really awkward support email asking them to reverse the charges, which they did fortunately.