The mother Flan is teaching her child an important lesson... That torturing them until giving them a painful death makes their filling all the sweeter to eat.
See it like a documental, aka, don't feel that bad, it's nature, you can't do anything, eat or be eaten, like how when national geographi show lions hunting or frogs eating bugs.
It may help you to not feel bad, since natural predators do some "training play" with their preys for teaching their cubs, many times felines let a slightly weakened prey to run in a controlled aread so the cub can practice.