In a pre-taped package, Arnold explained that the inspiration behind the dance was the close bond that they've formed throughout the season.
"He truly has become the older brother to me that I always wish I had," Arnold told the DWTS cameras, before she suffered a painful injury while rehearsing a number with her fellow pros the day before the live semifinals episode.
"I was practicing the pro number and I literally just stepped up onto a stair and it felt like my whole leg gave out and stopped working," Arnold recalled. "I'm just nervous that it's going to happen again, and it's the semifinals and I want to dance it with Jordan and I hope this doesn’t stop me from doing that."
Luckily, it didn't stop her at all. In fact, the pair went on to deliver two of the night's most impressive performances -- including their second dance of the episode, a jive set to Tina Turner's "Proud Mary."
As Arnold revealed after the dance, she wasn't the only one to have to power through an injury this week -- Fisher ended up getting hurt as well when his pro partner accidentally stabbed him in the eye with her nail.
"We wouldn't all love an eye injury this late in the season, and unfortunately that happened today," Fisher told co-host Erin Andrews after their dance. "[I got a] scratched cornea. A nail went in my eye earlier today."
While he explained what happened, Arnold sheepishly held up her hand to display her colorful nails.
"So we're shot up and on medication and the whole thing right now!" Fisher admitted, laughing.
"I feel like this dance represented the struggle that we went through today," Arnold chimed in, before she started to get choked up. "I wanted this dance to represent the relationship that we've formed and the journey that we've gone on together, and I really appreciate him. He's stuck it out with me throughout this entire thing."
For their first dance, the couple earned a 28 out of 30, and then a perfect 30 for their second, for a combined total of 58 out of 60.
The dancer revealed that she tore a muscle in her leg while doing the splits during rehearsals early Monday morning, and that producers were thinking about having her sit out, but she refused.
"[I told them], 'You're gonna have to drag me off that stage, because I am dancing with Frankie! I'm gonna be there for him,'" Carson told Andrews after the couple performed their first dance of the night -- a salsa set to "Shake" by Yin Yang Twins.