Zuckerberg agreed to the hearings as pressure mounted over the Cambridge Analytica scandal and the company's own admission a year ago that it had been compromised by Russians trying to influence the 2016 election.
For Zuckerberg, who often found himself explaining what his company does in rudimentary terms to lawmakers twice his age, the hearings could be considered a win: Facebook shares rose more than 1 percent after climbing 4.5 percent on Monday. FaceMash was a prank website that I launched in college, in my dorm room, before I started Facebook.
Shares are down 16% from the all-time high that they hit before the Cambridge Analytica data scandal, which Facebook now says has affected 87 million users, first came to light. Pallone called the response "disappointing". "If all we do is have a hearing then nothing happens that's not accomplishing anything".
Wearing a dark suit and tie and prefacing nearly every remark with "Congressman" or "Congresswoman", Zuckerberg appeared even more controlled than he did on Tuesday, as he refrained from cracking jokes and flashed few smiles.
It is now on record that Facebook collects data about non-users and Zuckerberg has no idea how much data is stored without consent or specifically how it is used.
Zuckerberg said he accepted that legal restrictions of some sort were in the cards - while adding a word of caution.
Zuckerberg responded that the company had made mistakes, but that "we try not to make the same mistakes multiple times".
One email, which was sent to private addresses associated with the duo's Facebook accounts, explained that the website had introduced new guidelines for accounts eligible to earn money through Facebook in September of previous year.
Republican congressman Fred Upton cited an example of a Michigan Republican whose campaign page was removed from Facebook. "Those posts he brought up on the screen were brought to Facebook's attention back in November, but they hadn't taken any action". "I know of no surveillance organization that allows people to delete data". "You know there are people in Russian Federation whose job is to exploit our systems... so this is an arms race", he said. Yes, Zuckerberg answered unequivocally.
Mr Zuckerberg was on Capitol Hill for the second time in two days to answer questions about data privacy. "But we were slow at identifying the type of - of new information operations". And while there are grey areas and nuances here, Facebook is right by and large.
Facebook's CEO repeated the company line defending its introduction of a messaging app for very young children: It just wants to provide a way for parents to keep in touch with their children.
Senator Ted Cruz (R. -Texas) confronted Zuckerberg about alleged bias and censorship of political and religious content on the technology platform, saying Facebook "has blocked over two dozen Catholic pages" as well as conservative content "after determining their content and brand were, quote, 'unsafe to the community'".
Representatives are also on average younger than senators, which could-but doesn't have to-translate to a better appreciation of the nuances of the internet and social media.