[common among Mac users] SCSI interface hardware is notoriously fickle of temperament. Often, the SCSI bus will fail to work unless the cable order of devices is re-arranged, SCSI termination is added or removed (sometimes double-termination or no termination will fix the problem), or particular devices are given particular SCSI IDs. The skills needed to trick the naturally skittish demons of SCSI into working are collectively known as SCSI voodoo. Compare magic, deep magic, heavy wizardry, rain dance, cargo cult programming, wave a dead chicken, voodoo programming.
While ordinary mortals frequently experience near-terminal frustration when attempting to configure SCSI device chains, it is said that a true master of this arcane art can (through rituals involving chicken blood, ground rhino horn, hairs of a virgin, eye of newt, etc.) hook up your personal computer with three scanners, a Zip drive, an IDE hard drive, a home weather station, a Smith-Corona typewriter, and the neighbor's garage door.