A favorite pastime of Urban and Suburban children.
The child will knock on an unsuspecting victim's door, but before the victim has time to answer, the "knocker" will dissapear in similar fasion to a ninja.
Tyrese: Yo brotha, let's go ninja knocking.
Tyrone: Wurd up dawg, ima say we get the ol' bitch down the alley.
Tyrese: Hellz ya mother fool
Something that occurs when combustion of some of the air/fuel mixture in the cylinder does not result from propagation of the flame front ignited by the spark plug, but one or more pockets of air/fuel mixture explode outside the envelope of the normal combustion front.