During my stay at Dreamworks working on Shadows I was borrowed by the Turbo production for a couple of weeks to animate a couple of hand drawn shots for one of the sequences. The idea was that the character who owned Turbo needed to have money to pay to enroll the snail in a car racing competition and he takes the money saved by his brother from their Taco stand restaurant.
He knows he did a bad thing and did not have a clean conscience after that. In the shots I did he looks at the taco restaurant's logo and one of the tacos, that represented his brother would talk to him as if it was his conscience saying he did a bad thing to his brother.
I thought it was a great idea and it could have been fun to see it in the final film but they decided it was not and dropped them from the final version.
The other day I saw a scene from the Sopranos where a fish in a farmer's market talks to the character of Tony Soprano as if it was his conscience playing with him.
So, there you go.