Lupita Nyong'o damaged her vocal cords so badly doing a happy robot voice on 'The Wild Robot' that she almost needed surgery

• Lupita Nyong'o voices the main character Roz in "The Wild Robot," in theaters Friday.
• Nyong'o strained her vocal cords, forming a polyp while recording Roz's robotic yet emotional voice.
• Recording sessions were halted for three months to allow Nyong'o to recover without surgery.

DreamWorks Animation's new movie, "The Wild Robot," is an emotional story about a utilitarian robot named ROZZUM ("Roz" for short) who finds herself on an island and discovers that her purpose goes far beyond what she was built for.

Voicing a robot who gradually becomes more human also ended up being a physically taxing experience for actor Lupita Nyong'o, who took pains both figuratively and literally to create a voice for Roz that could be both robotic and emotional.

"Lupita didn't just show up and read the script; she absolutely took apart the idea of, who is this robot?" "The Wild Robot" director Chris Sanders told Business Insider.

"She needed to understand all of this so she could craft the proper voice," he added. "It was a fascinating journey watching her dissect the character piece by piece. It was not simple for her."

As a result, Nyong'o's vocal cords paid the price.

At one point in her recording sessions, which took years to complete, Sanders was notified that Nyong'o needed to go on vocal rest. She'd strained her vocal cords so much doing Roz's voice that they formed a polyp, a growth on the vocal cords that forms due to overuse or misuse.

"I wasn't even aware, honestly, of the stress she was putting on her own voice," Sanders said. In retrospect, he added, it makes sense — Roz should have a "programmed optimism" in her voice when she first arrives on the island, and Lupita achieved that by straining her voice. "She did suffer wear because of that," Sanders said. "And I didn't even know it."

Nyong'o revealed on "Late Night with Seth Meyers" in June that doing the "super-positive" Roz voice for weeks at a time led to the polyp. She was scheduled for surgery, but refused and focused on recovering by not speaking, halting her recording sessions for three months to ensure she could heal. She even wore a note that read, "I'm on vocal rest" when attending a Taylor Swift concert during that time.

Sanders, who's no stranger to voice work himself — he directed the Disney classic "Lilo & Stitch" and also voiced Stitch — said that he noticed how much care Nyong'o put into protecting her voice once she returned.

"She modified the recordings so she would avoid damage," he said. "She would rest her voice and hydrate her throat throughout the sessions, because she understood it was a marathon."

"The Wild Robot" opens in theaters on Friday.