large snake provides venom to sustain Voldemort

Lord Voldemort’s snake; her milk nourished Voldemort; Albus Dumbledore suspected that he may have been one of Lord Voldemort’s Horcruxes (GF1, 29, 33; HBP23)

Nagini is a fictional animal from the Harry Potter series. She is a snake and the pet of Lord Voldemort, a Parseltongue, who is capable of communicating with her.