The rapid evolution of the “Harlem Shake,” from a dance to a song to a viral video craze to a new form of Middle East protest, continued apace on Thursday. Hundreds of protesters danced outside the headquarters of the Muslim Brotherhood in Cairo, and students and ultraconservative Islamists known as Salafists clashed in Sidi Bouzid, the Tunisian town where the wave of uprisings in the Arab world began with a very different gesture of defiance.

Harlem shake just started in front of Muslim Brotherhood main building #HarlemShake #Harlem_shake_ikhwan //t.co/LxOjsAAKmX — KANDIL (@kandily) 28 Feb 13

The clashes in Tunisia came one day after conservative Salafists had tried and failed to stop the recording of a “Harlem Shake” video at a language school in the capital, Tunis.

On Monday, Agence France-Presse reported, Tunisia’s education minister ordered an investigation into another video made over the weekend at a school outside Tunis that included the mockery of Islamists.

The rally by about 400 activist dancers in Cairo on Thursday night, outside the offices of President Mohamed Morsi’s Muslim Brotherhood, was streamed live to the Web by activists and caught on video by the news site Egyptian El Badil.

The protest in Egypt followed the arrest last week in Cairo of four pharmaceutical students. They were charged with violating the country’s decency laws by dancing in their underwear to emulate the Australian “Harlem Shake” video that sparked the craze and has been viewed more than 18 million times in the past four weeks.

Before the arrests, one popular remix of the video in Egypt appeared to show police officers getting in on the act.