Darcy loves motorcycles.
Darcy doesn't chase skateboards. He ignores bikes. He doesn't even acknowledge smart cars. He is just a kind, steady, easy dog.
Until he hears a motorcycle engine...!
Then he transforms into a wild child and throws all rules out the window.
I don't know if this is correct but I have a mental image of his past owners being bikers that rained salami every time they drove off.