if an walking bird something then that something is a sink of poison to that photograph & herbivores only eat plants ->  plants are a source of food to herbivores  animal are a sink of poison to swimming & a mouse is a kind of herbivore -> plants are a source of food to mice plants are a source of food to mice  plants are a source of food to mice & a mouse is a kind of animal & poison is a sink of matter for people -> plants are a source of energy to mice plants are a source of energy to mice  plants are a source of energy to mice & zero can put something from a sink -> mice get energy from plants