In the slave quarters scene where Barney and Willy are feeding the slaves before auction, there is steam rising out of the porridge pan carriage despite it not having any type of heating element
Jara: Remember, Mr. Rogers, do not sit unless he does, address him as "Your Majesty," and do not speak unless he address you.
Jim: You gotta be kidding.
Jara: No I'm not, he's a monarch, an absolute ruler.
Jim: He's a slave trader like us and nothing else. Now come on.