Besides alcohol, there apparently is another nasty among us that can cause serious liver damage in humans, not to mention rats. Comfrey, Symphytum officinale, is an herbaceous perennial plant commonly grown in gardens. Its leaves are sometimes eaten, but most often they are used in brewing a tea for which its devotees claim a long list of benefits.
Comfrey contains a number of pyrrolizidine alkaloids, which are the damaging agents.
They are in fact the same compounds in tansy ragwort, an invasive pasture weed which has been implicated in more than a few deaths of farm animals. This one, too, destroys the liver. Another reason for not introducing comfrey to the garden is that is usually becomes one of the most vicious weeds ever encountered. Any broken-off piece of its substantial root system has the capacity to regenerate a brand new plant. It's a lot like bindweed or wild morning glory, and quackgrass, in this respect.