DETONATION (KNOCK)
-A/F ignited after spark due to heat and pressure
-burns about 6x faster when this happens
-caused by too much spark advance, too low octane
-occurs under low load/low RPM

The extra heat created by this will melt pistons and spark plugs and crack the cylinder walls. Also, the shockwaves created by the force of this explosion rattles the pistons around in their bores creating the knocking sound.

Here is a good thread to get you going: http://www.honda-tech.com/zerothread?id=328862