Use of index [0] in random.choices()

What is the purpose of using [0] in random.choices()? Does [0] refer to index of Lists or of its sub-lists in the example code below? If I use [0], I get the single random word from the lists, which is the desired result, but if I omit [0], it gives the random sub-list with all of its elements.

Why it is giving the different result for the two cases?

If I try [1] instead of [0], The code gives

index error: index out of range

But if I use [0] or [-1], code gives the desired result.

import random

Animals = ["Cat", "Dog", "Lion", "Tiger", "Elephant"]
Fruits = ["Apple", "Orange", "Banana", "Mango", "Pineapple"]
Vegetables = ["Tomato", "Potato", "Onion", "Brinjal", "Peas"]

Lists = [Animals, Fruits, Vegetables]

word = random.choice(random.choices(Lists)[0])

print(word)