He grabbed his wife, Jill’s, hand to his right and said, “This is my little sister, Valerie.” Jill Biden began waving her hands and said, “No, no,” as she couldn’t contain her laughter. Before realizing his mistake, he grabbed his sister to his left and said, “And I’m Jill’s husband.”

His eyes widened as he saw it was actually his sister to his left. “No — you switched on me!” Biden said.

“This is my wife. This is my sister,” he said, pulling the two into an embrace. “They switched on me.”

After laughing off the mistake, Biden quickly transitioned to listing the states he’d won so far on Super Tuesday.

“Just a few days ago, the press and the pundits declared the campaign dead,” Biden said as supporters booed. “And then came South Carolina. They had something to say about it.”

Biden continued: “And we’re told, well, when you get to Super Tuesday, it will be over. Well, it may be over for the other guy. Tell that to the folks in Virginia. North Carolina. Alabama. Tennessee. Oklahoma. Arkansas. Minnesota. And maybe even Massachusetts. It’s too close to call. We’re still waiting for Texas and California, a few other small states to come in. But it’s looking good. So, I’m here to report, we are very much alive.”

The rally took an unexpected and momentarily volatile turn when two protesters stormed the stage from behind, holding “Let Dairy Die” signs. Campaign staff, including the Biden adviser Symone Sanders, grabbed the protesters and hauled them off the stage. Sanders later posted on Twitter: “I broke a nail.”

As a slightly frazzled Biden continued with his speech, both his sister and his wife, who had moved to stand between the candidate and the second protester, were visibly unsettled by the altercation.

The animal rights group Direct Action Everywhere claimed responsibility for the demonstration, and named the protesters as Sarah Segal and Ashley Froud. The group has appeared at other political rallies, including campaign events for Bernie Sanders, where protesters have grabbed microphones and poured red liquid meant to look like blood. Some protesters appeared shirtless during a Sanders rally in Richmond, Calif., with “Let Dairy Die” written on their chests.

The animal rights group said in a statement that the protesters targeted Biden after his support for legislation favorable to big agriculture.

The disruption didn’t put too much of a damper on Biden’s energy, as the former vice president jumped back into his speech and launched his attacks on President Donald Trump’s character. Supporters chanted, “Let’s go, Joe!”

“Let’s get back up. We are decent, brave, resilient people,” Biden said, his voice rising again. “We can believe again, but we are better than this moment. We are better than this president. So get back up and take back this country. The United States of America. There is not a single thing we can’t do.”

Matthew Choi contributed to this report.