I understand that the tear glands work all the time, to lubricate the eyeballs.
But why do they go into overdrive when we’re upset/angry? I don’t see why your eyeballs should need more lubrication because your mother has just died, for instance. But people who are upset cry to the extent that tears flow down their faces. Does anyone know (or have a plausible theory) why? And do any non-human animals cry when emotionally stressed?