When Percy is back at the sheds covered in chocolate, Henry says "Choc-ice on wheels." This is a racial slur used to describe someone who is figuratively black on the outside and white on the inside. However, this cannot be a character error because the engines in the series do not have a race associated with them.
Henry says "Choc-ice on wheels" when Percy is covered in chocolate. "Choc-ice" is a racial slur, which refers to someone being black on the outside and white on the inside. However, the engines in the series do not have a race associated with them.