Former Housing and Urban Development Secretary Julián Castro had the most tweeted moment of Thursday night's debate with a pointed comment aimed at former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE that drew gasps and jeers from the live crowd and seemed directed at the former vice president's age.

Castro repeatedly asking Biden if he had forgotten what he said "two minutes ago" was the most-tweeted part of the debate, according to Twitter.

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"Are you forgetting what you said two minutes ago?" Castro asked Biden as the two battled over details of Biden's health care plan and whether people would be automatically enrolled in it.

"Are you forgetting what you said two minutes ago?" Castro repeated. "I can't believe that you said, two minutes ago, that they had to buy in and now you're forgetting that. We need a health care system where you're automatically enrolled."

Julián Castro goes after Joe Biden: "Are you forgetting what you said two minutes ago" https://t.co/4PJW39UOgD pic.twitter.com/UxHvZnvz3g — The Hill (@thehill) September 13, 2019

Biden leaned into Sen. Bernie Sanders Bernie SandersSirota reacts to report of harassment, doxing by Harris supporters Republicans not immune to the malady that hobbled Democrats The Hill's Morning Report - Sponsored by Facebook - Republicans lawmakers rebuke Trump on election MORE (I-Vt.) as Castro spoke, perhaps to ask what he had said. Some of Castro's remarks may have been difficult to hear over the noise of the crowd, which included a number of people expressing shock or displeasure with the remark.

After the debate, some Democrats called Castro's attack on Biden's memory too harsh and personal.

Castro said it had just been a discussion about health care.

The second-most-tweeted exchange of the debate also featured Biden and a remark by the former vice president that seemed to speak to his 76-year-old age.

Biden, the 2020 Democratic front-runner, urged parents to "make sure you have the record player on at night."

"Play the radio, make sure the television, excuse me, make sure you have the record player on at night..." @JoeBiden said in response to a question on reparations in Thursday's #demdebate. https://t.co/8qrciSSAlH — Twitter Moments (@TwitterMoments) September 13, 2019

Biden was tweeted about the most out of the 10 candidates on stage in Houston, followed by tech entrepreneur Andrew Yang Andrew YangBiden's latest small business outreach is just ... awful Doctor who allegedly assaulted Evelyn Yang arrested on federal charges The Hill's Campaign Report: Biden weighs in on police shootings | Who's moderating the debates | Trump trails in post-convention polls MORE.

Yang generated interest after unveiling a proposed plan to give away $1,000 per month for a year to 10 families chosen at random.

Sanders was the third-most-tweeted candidate of the night, followed by Sen. Elizabeth Warren Elizabeth WarrenOvernight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds On The Money: Half of states deplete funds for Trump's 0 unemployment expansion | EU appealing ruling in Apple tax case | House Democrats include more aid for airlines in coronavirus package Warren, Khanna request IG investigation into Pentagon's use of coronavirus funds MORE (D-Mass.) and Sen. Kamala Harris Kamala HarrisTexas Democratic official urges Biden to visit state: 'I thought he had his own plane' The Hill's Campaign Report: Biden on Trump: 'He'll leave' l GOP laywers brush off Trump's election remarks l Obama's endorsements A game theorist's advice to President Trump on filling the Supreme Court seat MORE (D-Calif.).

Ratings for the debate on ABC will be available Friday afternoon.