At the end, after Superman is shot by the crooks, he lunges toward them, he kicks up a grass mat set piece and rolls it over.
You can clearly see Superman's arm muscles flexing as he is pulling on Carmalitta's (the burro's) rigging to make her nod her head- more so on the second camera angle.
He asks the Burro how far away Jimmy and the others are away from the Jail and asks her how many miles away (7), he should have asked how many kilometers away since they are in Mexico.