如何在Django中为模型获取具有反向关系的所有类的集合？

Given:

from django.db import models

class Food(models.Model):
     """Food, by name."""
     name = models.CharField(max_length=25)

class Cat(models.Model):
     """A cat eats one type of food"""
     food = models.ForeignKey(Food)

class Cow(models.Model):
     """A cow eats one type of food"""
     food = models.ForeignKey(Food)

class Human(models.Model):
     """A human may eat lots of types of food"""
     food = models.ManyToManyField(Food)
from django.db import models

class Fo