Does just thinking about killing someone create dab karma? When you understand karma as cause and effect, you will see that evil thoughts indeed accumulate karma. Merely by dwelling on the idea of killing someone, you put into motion a causal relation with repercussions. These kinds of thoughts constitute one’s mental life, and if there is sufficient accumulation they can manifest in speech or action. In the sutras the Buddha says that in the world of samsara there is not a single action or even giving rise to thought that is excluded from creating karma. Whatever sentient beings do or think is centered on attachment to self, and because of this they continue to create karma. Therefore, when we even have thoughts of killing, as Buddhist practitioners we should give rise to a sense of contrition and practice repentance.

Generally speaking, when one engages in negative actions (the cause), one will reap negative results (the effect). This is the causal result of bad karma. Correspondingly, when one engages in virtuous actions, one will reap virtuous results. This is the causal result of virtuous karma. There is another kind of karma that is neither good nor bad, and I'll get to that later. Speaking generally however, karma can be good, bad, or neutral.

With karma that is neutral the determining factor is the state of mind while engaging in such actions, whether there are subtle leanings towards wholesome or unwholesome. There will still be retribution tilted towards good or bad, but it will be mild. However, there are genuinely neutral karmic actions, with neither wholesome nor unwholesome overtones, and the retribution that results will be neither good nor bad.

Depending on their karma sentient beings can be reborn in one of six modes or realms2 of existence. A sentient being that engages in wholesome actions will receive retribution by being reborn in one of the three upper realms--the human realm, or one of the two heavenly realms. A sentient being that engages in unwholesome actions will receive retribution by being reborn in one of the three lower realms--the animal realm, the realm of angry spirits, or most severely the hell realm. Thus one's accumulated karma determines where among the six realms, and what form they will take at the next rebirth.