Natural sources of salt used by porcupines include different salt-rich plants ( such as yellow water lily and aquatic liverwort ) , fresh animal bones , outer tree bark and mud in salt-rich soils . Natural sources of salt consumed by porcupines include varieties of salt-rich plants ( such as yellow water lily and aquatic liverwort ) , fresh animal bones , outer tree bark , mud in salt-rich soils , and objects imbued with urine .