A mathematics university professor discovered the hard way that silence isn’t always golden.

After delivering a Zoom lecture for two hours, Professor Dong Wang of National University of Singapore soon realized that none of his students heard a word because his mic had been muted, the local Independent news outlet reported.

Wang then called for questions from the roughly 20 students who actually stayed connected to the online class throughout the whole thing — and got nothing but crickets.

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“No … uhhh … we can finish our class?” he asked.

Eventually, a few students spoke up and told him he had been on mute the whole time.

“We cannot hear anything from you since 6:08,” one student told the flummoxed prof.

“From what?” Wang asked the student, who confirmed the time. “You mean, how long did you hear?”

A student answered that they only heard a little at the beginning, at 6 p.m., and nothing else from 6:08 p.m. on as his screen froze.

A clearly rattled Wang then told the class that he’d repeat the entire lecture another time.

Azusa Chan, one of the students, told the news outlet that the professor inexplicably muted himself.

“Students tried all sorts of things to get his attention by unmuting and even calling his phone number. However, he did not respond and continued with the lesson,” the student said.

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“The participant count dwindled as time went on, as students could not contact the prof and had no other recourse. What you see here are 20+ students who waited patiently for two hours for the prof to come back,” Chan added.

The student explained that Wang was doing the entire lesson on an iPad, “so you can expect many things to go wrong on such a setup.”

“After this incident, he left [sic] his phone beside him whenever he is conducting a lecture so we could call him in case of emergency,” Chan said.