The rat realizes he has the power to do whatever he wants.
“Should I get revenge on my oppressors or help my bretheren?” The rat thought
There were benefits from both. He could make the family of the boy understand what it truly feels like to be small and insignificant or even a pest by shrinking them and their house. But also, other rats are hurting from the humans too
No more dumb accusations of being a plague vector for the species. Humans were always the plague vector.
Rats could even become dominant species like they truly wanted to be or even wipe out the human race at will.
But at what cost? Well it didn’t matter as the rat wanted revenge.