Mecum Rule?

[Mr70]

While watching the auction last week,someone bid,and the hammer yelled "Mecum Rule...Mecum Rule".
It was hard to listen to over the TV announncers and I thought it was a joke,but it looked/sounded like they accepted a bid by the same previous bidder seconds earlier,meaning he just raised himself.

Is that true?....meaning if a bidder raises his own bid because he's not paying attention,and offers the next amount being asked for,Dana holds you to it.

Do anyother car auction houses do this too?..because I was surprised they were labeling this "Mecum Rule".