How do they get that crackle sound in breakfast cereal?

Also, of course, the snap and p.

A related question: is there a metric or a method of cereal manufacture that can be used to rate when the cereal gets mushy? This is a real question; I would be willing to bet that the food giants’ research departments go into this topic.

You would win that bet.

As for your first question, these guys have a good guess:

I stumbled on the following cite, on my hard drive since before the thread went underground, but somehow with all the fuss after 2/21/2010 it never made it.

According to Kimstu’s source (the JOIR), the test method used a Mettler LP16 moisture balance, an Instron 1122 Universal testing machine, and a piston-driven capillary rheometer.

The techniques used (I am not able to judge the results) are quite different.

INFLUENCE OF WATER ACTIVITY ON THE ACOUSTIC PROPERTIES OF BREAKFAST CEREALS

EWA GONDEK1, PIOTR P. LEWICKI1, and
ZBIGNIEW RANACHOWSKI2
Article first published online: 22 SEP 2006
Journal of Texture Studies
Volume 37, Issue 5, pages 497–515, October 2006

ABSTRACT
Corn and wheat bran flakes were compressed in a plastic cylinder and the generated vibrations were measured by a piezoelectric accelerometer. Amplitude–time records were thoroughly analyzed and the total acoustic energy in arbitrary units, number of acoustic events and energy of a single acoustic event were calculated. Relationships between the time of compression, frequency and sound intensity are presented as acoustograms. All parameters, except the energy of a single acoustic event, were strongly dependent on water activity (Aw). The flakes differed essentially in their ability to propagate vibrations. At low Aw’s, both types of flakes were alike, but at higher Aw’s, corn flakes damped high-frequency waves while wheat bran flakes did not show this property.

Suffice to say that the quieter your cereal the better for you …

Its a form of murphies law, If it tastes (or looks or sounds) good, it is bad for you.