Story highlights Driver hauls dog atop open trailer traveling down Florida interstate

Flagler, Florida, authorities are investigating the case

(CNN) A dog who was captured on video while chained to the top of a trailer traveling along a Florida interstate is OK.

Brenna Cronin and her boyfriend were driving near the Flagler exit on Interstate 95 on Wednesday when they saw the "shocking" sight. A dog was standing atop a crate carrying another animal.

"We saw a dog chained to a crate. I had never seen anything like that before," Cronin told CNN. "I was completely appalled and disgusted."

As the SUV barreled down the interstate at high speeds, the dog cowered, exposed to the open air. It had an "S" branded into its back leg, she said.

"As I was filming the dog and he saw me, he stood up and looked so scared. You know when dogs are happy, they have their tail wagging and a big smile. He was terrified," Cronin said.

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