He is being asked a lot of specific data type questions that I wouldn't expect him to know off the top of his head so I can't really fault him for that. I wouldn't really call his speech stuttering though.
His answer about the tracking program was interesting though. It wasn't a complete denial and it sounds like it would be significant enough of a tool that he would know about it if it did exist but then again, for such a massive company maybe he wouldn't? Not sure. Of course he doesn't want to get caught in a lie so saying "I don't know" is always going to be the safest answer just in case.
Go back ans look at his previous testimonials. He did the same thing REGARDLESS of the question.
The last one about a week or 2 ago, he was there to answer whether FB has a bias which causes them to ban CONSERVATIVES and censor CONSERVATIVE CONTENT more often than non-Conservative.
He was asked -- not for the first time -- if he can name ONE high profile Liberal FB member who was either banned or had their content cesored. This, after Cruz rattled of several members of government and the media who were Conservative or anti-Democrat, and were banned locked out, and/or censored.
Zuckerberg said, "Not off the top of my head."
#1, that's bullshit. If there was one, it wuld have made headlines JUST LIKE the ones Cruz listed.
#2, he knew what the topic of the hearing was. Did he, nor his lawyers, not predict that such a question was possibly going to be asked?
Let's review. Topic: Censorship tends to be AGAINST Conservatives and NOT Liberals. He was asked to name ONE Liberal out of all the people being banned. Didn't have a name.
Yeah, this is not a "data type question." Doesn't take a database search to know if someone high profile like Rosie O'Donnell or Kathy Griffin was EVER censored.