The poetic example does not rely on one identical property throughout. Pearls suggest the sheen and clarity of tears; narcissi suggest the eyes’ appearance; hailstones suggest the brightness of teeth.
Identifying the ground of resemblance is important. If hailstones stand for teeth, simply saying “coldness” misses the most relevant visual relationship.
One line can contain several distinct metaphors, with a separate intended referent and relevant resemblance for each.