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

Question

In Monsters University, during the Scare Final, Dean Hardscrabble tells Sullivan that roaring at a child for whom it is not the appropriate scare...

...wouldn't make him scream, it 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.") and the Monsters don't appear to bring any equipment with them into the Human world (definitely nothing like the scream extractor Randall builds in Monsters, Inc.). Indeed, they seem careful to leave any Monster artefacts behind before entering a door (as Frank McCay does with his MU cap). So I was thinking that perhaps the child's room itself is 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).

Do the Monsters have some way to completely extract the scream the child produces, preventing it from reaching the parents' ears?

Answer 1

There is nothing to suggest this, except that speech.

I think Hardscrabble is simply trying to drive home the point of Sully's lazy work ethic. Every scream can possibly alert parents, but the scream power is what they're after. Once it's had a monster can jump right back through the door and the risk is completely minimized. If Sully gets a crier because he hasn't even bothered to read up, he's upping the risk and then either has to double down and try to wrangle a scream with the parents maybe already on the way, or abandon the mission and go back through the door without anything benefiting the Monsters world.

Sully is bungling the entire scarer job when he's stepping into another world and assuming that risk, and not caring to do it right. Hardscrabble is just beating the point in with a mallet.

Answer 2

The scream of a child is absorbed for its energy but is still able to be heard by the child's parents. The scream does alert parents but unlike sobbing, the monster did gain the energy it came for. There doesn't appear to be any particular technology preventing the parent from hearing anything.

• From a resource management standpoint, getting the scream makes the creation of the portal to the child's room pay for itself and net a return on the energy investment.

  • If on the other hand, the child cries, it will still alert the parents but the Monster gets nothing, energy is expended and the trip is a bust.

  • This may also reduce the chance they will be able to get energy from that room again and a new door will probably need to be created, thus losing a natural resource provider and having to find a new child.

  • The energy required for the discovery of new children has not been shown but is likely to be considerable, just like the acquisition of most natural resources are.