Former Special Counsel Robert Mueller was frequently tripped up and forced to ask lawmakers to repeat their questions during his rapid-fire questioning on Capitol Hill on Wednesday, though he reportedly prepared at length for the hearings.

At one point, he even said he wasn't familiar with Fusion GPS, the opposition research firm behind the controversial anti-Trump dossier.

The longtime lawman was known to be reluctant to testify, having made clear he would largely stick to the boundaries of his original report. He reiterated Wednesday that his testimony before House committees would be based on the text of his report on Russian election interference and potential obstruction of the investigation.

But that didn't stop a barrage of detail-rich questions that seemed to throw off the usually stone-faced investigator.

House Judiciary Committee Ranking Member Rep. Doug Collins, R-Ga., focused his questions on the former Special Counsel's findings that the investigation did not establish any conspiracy between President Trump and Russia. Collins asked Mueller if "conspiracy" and "collusion" were colloquially the same thing, and Mueller said no. Collins then quoted Mueller's own report, which indicated otherwise.

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"As defined in legal dictionaries, collusion is largely synonymous with conspiracy as that crime is set forth in the general federal conspiracy statute," Collins read from the report. "Now, you said you chose your words carefully. Are you contradicting your report right now?"

"Not when I read it," Mueller replied, prompting Collins to ask, "So you would change your answer to yes?"

"No, no, the uh, if you look at the language," Mueller said before trailing off.

Collins pressed further, saying, "I'm reading your report sir. It's a yes or no answer."

Mueller asked for the page number of the report, then stammered before saying he would "leave it with the report." When Collins stated that the report says that the terms "collusion" and "conspiracy" are synonymous, Mueller said, "Yes."

Mueller appeared flustered by Collins' questioning, although the congressman admitted he has a tendency to speak quickly. Collins said he would try to speak slowly, but still maintained a rapid pace during his five-minute grilling.

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Nevertheless, Mueller appeared off his game even after the fast-talking Collins was done.

Rep. Zoe Lofgren, D-Calif., went next, speaking at a more deliberate pace. After her first question about the extent to which Russia interfered in the 2016 election, Mueller responded, "Could you repeat that, Ma'am?"

At another point, he asked GOP Rep. Jim Sensenbrenner what he was reading from.

"I'm reading from my question," the Wisconsin lawmaker shot back, before Mueller again asked him to repeat his question.

Later in the day, when he appeared before the House Intelligence Committee, Mueller told a lawmaker his office does not use the word “collusion” because it “has no relevance to the criminal arena.” He then noticeably struggled to recall the correct word, at which point Vermont Democratic Rep. Peter Welch suggested the word “conspiracy” and Mueller replied, "That’s exactly right.”