He's convincing because that part of Robert David Hall's performance is not acting.

Hall, who played Dr. Al Robbins in more than 300 episodes of the beloved procedural drama (the third-highest episode count of anyone in the cast) actually has two prosthetic legs (like his character) and walks with a crutch.

Hall is an advocate for disabled people and laments the fact that, while he has had great success as an actor and has even been able to incorporate his disability into the roles he plays, many disabled people face discrimination.

However, he's pleased to have provided a positive example — one seen by millions — of what a disabled person is capable of (with his character just as hyper-capable in his field as the other geniuses).

"Hopefully people can see me and see that I'm not sitting around moping with my head in my hands," he told OnMilwaukee magazine in 2006.

He did mention in another interview that he's also happy the prosthetic legs and the limp in no way define Dr. Hall. "It's about your ability," he told the Seattle Times, "not your disability."

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