Why wouldn't a scream alert the child's parents, if crying can?

In Monsters University, during the Scare Final, Dean Hardscrabble tells Sullivan that roaring at a child for whom it is not the appropriate scare "would make him cry, alerting his parents, exposing the monster world, destroying life as we know it".

Although the second half sounds a bit far-fetched (perhaps an attempt by Hardscrabble to really drive the point home to Sullivan), I'm left wondering about the first half. If a child's crying would alert the parents, why not a scream? The very beginning of the film shows that it doesn't take much for parents to come to check up on the child ("I thought I heard something."), so do the Monsters have some way to completely extract the scream the child produces?

As far as I can see, they don't bring any equipment with them into the Human world (definitely nothing like the scream extractor Randall builds in Monsters, Inc.). Is the child's room itself somehow modified to absorb specific sound waves and transmit them into the scream canister attached to the door station? That might explain why the first time a door is opened, it's done in an isolated, darkened lab environment (as can be seen during the orientation tour Mike attends on his first day at MU).