So we all know that twilight vampires cannot cry because of their unchanging state and physical properties , but the only reason given in the official guide is that vampires do not cry/ produce tears because " they exist to protect the eye from foreign objects. as none could harm a vampire's eye they do not need any" (roughly) , but as I'm sure anyone here who has cried or yawned before would know, that is not the only reason. tears are also emotionally caused and vampires are very emotional creatures so would they cry? human tears are made of 3 things: water, salt and mucus( and also may contain any stress chemicals needed to be flushed out, hence emotional tears) vampire tears could be made from a venom based substance...........
let me know what you think
I don't see any reason why Ms. Meyers could not have used a form of venom for them to cry emotionally.