Kendra Little explains the NOINDEX option of DBCC CHECKDB and how it relates to PHYSICAL_ONLY:
PHYSICAL_ONLY looks at page structures and makes sure something isn’t obviously wrong. If you have the database’s page verification option set to CHECKSUM (the default since SQL Server 2005, and a very good thing), it runs a checksum on the page and compares it to a checksum recorded in the header when the page was last modified.
When you use the PHYSICAL_ONLY option, you’re telling SQL Server to skip logical checks. It won’t do things like make sure the data in a clustered and nonclustered index on a table is consistent with one another.
I like the analogy, as well as the how-to guide on messing up your database. But try not to do that to a production database…