(CNN) -- When New York Mayor Michael Bloomberg appeared at a news conference Wednesday without Lydia Callis at his side, fans of the sign-language interpreter immediately expressed their disappointment via Twitter.
"Wait, where is Lydia Callis???? (aka our favorite sign language interpreter)" @abbygardner tweeted.
"Watching Bloomberg's latest briefing. So sad Lydia Callis is not the sign language interpreter #Sandy" tweeted @kyledoyle.
"Damn they change the #signlanguagelady ... WE WANT LYDIA CALLIS BACK !!!!" @JoeyStugotz6 posted.
Callis, 30, became an Internet sensation just three days earlier because of the dramatic facial expressions and body language she used to translate Bloomberg's dire warnings about the dangers coming with Superstorm Sandy.
Comedy Central's Jon Stewart, during Wednesday night's "Daily Show," said Callis's "expressive sign-language interpreting turned disaster press briefings into an Alvin Ailey sign-language recital."
"If you're in your home or somewhere safe where you can remain, stay there," Bloomberg said. "The time for relocation or evacuation is over. Conditions outside are dangerous, and they're only going to get worse in the hours ahead."
When the mayor talked about falling trees, high winds, heavy rain and rising waters, Callis made sure her face, hands and body conveyed the urgency to those who could not hear.
A falling tree took both arms to convey. One arm was the ground, and the other was the tree.
When Bloomberg warned "It is dangerous," viewers could see the danger on Callis' face.
As the mayor scolded two New Yorkers who had been arrested trying to surf the rolling waves of New York Harbor, calling it "just an outrage," the outrage was clear in her expression.
Several Tumblr accounts immediately appeared paying tribute to images of Callis signing for Bloomberg. Twitter postings of amazement erupted. Newspaper stories and online blogs soon followed.
New York magazine said Callis gave the city "a legitimate reason to smile" even as the storm loomed.
"The sign interpreter next to Bloomberg is basically his human emoticon set," @xeni tweeted Monday.
The mayor's news conferences became must-see TV for her new fans.
But Callis herself was staying out of the spotlight, apparently giving just one interview to DNAinfo.com reporter Jill Colvin, who tracked her down at the New York emergency management headquarters in Brooklyn on Wednesday.
"As you can see from when I'm interpreting, you see the tree falling, you see the building, you see the crane moving around," Callis told Colvin. "Because I need to have those pictures for the deaf people that need ASL," or American Sign Language.
Her dramatic expressions, gestures and body language are needed to communicate the urgent message, she said.
"Hearing people tend to not understand that deaf people need those facial expressions," Callis said. The body language replaces the intonation others hear in a voice, she said. "If I stand up there with a straight face and just interpret it, they're not getting half the message."
Callis said she tries to translate Bloomberg's emotions.
"When a reporter asks a sarcastic question, you can see it in my face," she said. "I'm like, 'Really — did you just ask that?' Because that's how the mayor is reacting in the tone of his voice. But I'm doing it on my face."
She told Colvin that she began signing as a child for her deaf mother and three siblings.
But Wednesday afternoon, Callis was gone, replaced by another woman whom Bloomberg introduced at his news conference as Pat Mitchell. She did not return for Thursday's briefing.
"Lydia Callis has been replaced! Feel bad for this woman signing now. Like trying to freestyle after JayZ has just performed," tweeted @janvijhaveri.
"Bloomberg's new signer does her job fine, but she doesn't have panache of Lydia Callis, who signed with a New York accent. Bring her back!" posted @MahaRafiAtal.
"Awww what happened? Bloomberg didn't like all the shine Lydia Callis was getting? Or did they just finally give her a break?" @DeePhunk wrote.
The mayor's office, obviously with bigger matters to address, did not respond to CNN calls or e-mails about Callis and her replacement.
Callis has remained mostly silent, not jumping into the New York media circus -- yet.
Silence is a job requirement, according to Kim Kurz, who chairs the American Sign Language & Interpreting Education department at the National Technical Institute for the Deaf.
Callis earned a degree in American Sign Language from that school, which is part of the Rochester Institute of Technology, before moving to New York City last year, a school spokesman said.
"We are honored to see Lydia's skills recognized in this situation and send her our best wishes for continued success in her profession," Gerard Buckley, the school's president, said in an e-mail to CNN.