One man was flapping his hands in fraud while the other was flapping his gums in fraud.

While Obama was flapping his gums ...

A fake sign language interpreter took to the stage during a mass memorial for anti-apartheid leader Nelson Mandela, gesticulating gibberish before a global audience of millions and outraging deaf people across the world.

DeafSA, South Africa's leading deaf association, condemned the presence of the unknown man at the memorial, which was attended by President Jacob Zuma and scores of world leaders including U.S. President Barack Obama.

While dignitaries were addressing the crowd in the 95,000-seat Soccer City stadium, the young, suited man with an official security pass round his neck produced a series of hand signals that experts said meant absolutely nothing.

Besides the bizarre twist to an event that also saw Zuma booed and jeered, the man's presence on the stage within yards of Obama and Brazil's Dilma Rousseff raised awkward security questions.

Somehow it's fitting.