http://docs.mongodb.org/manual/reference/program/mongoexport/#cmdoption--authenticationDatabase

If you do not specify an authentication database, the mongoexport assumes that the database specified as the argument to --authenticationDatabase holds the user’s credentials.

Surely this should be

If you do not specify an authentication database, the mongoexport assumes that the database specified to export holds the user’s credentials

Also, I'm not sure why this links to the mongotop documentation (which has the same erroneous paragraph, but not any extra detail)