What is the natural and probable consequences doctrine in the context of second degree felony-murder?

which "operates independently of the second degree felony-murder rule." (People v. Karapetyan (2006) 140 Cal.App.4th 1172, 1178.) "The natural and probable consequences doctrine does not merge all assaults into the felony-murder rule. Rather, it is a theory of liability for murder that applies when the assault has the foreseeable result of death. For aider and abettor liability, it is the intention to further the acts of another that creates criminal liability and not the felony-murder rule. [Citation.]" (Id. at p. 1178.)