When Phyllis Stanwyck hits Audrey MacMurray with the tyre iron, it is clean but in the next shot it is covered in blood.
When Harriet slaps Audrey, Audrey's helmet switches hands several times.
Sadly as a classic car professional a brake line travelling vaguely through the engine compartment is frankly, ridiculous, especially on a race car.
Then to cap it all this car has cable brakes, it does not have fluid brake lines, hence the plot line is completely inaccurate.
Use a pair of bypass garden pruning shears in place of tin snips to cut brake line as if such would be found in a mechanics pocket or lying around in a garage.