During Judge Brett Kavanaugh’s testimony and questioning last week before the Senate Judiciary Committee regarding sexual assault allegations against him, the word “beer” came up 53 times and the word “drinking” came up 43 times.

Though not ordinarily a theme in a Supreme Court nominee hearing, the question of what kind of drinker Kavanaugh was — and what he may have done under the influence of alcohol — emerged as one important, and disturbing, focus.

Kavanaugh suggested that while he liked beer, and sometimes drank a little too much, he never blacked out. Instead, he painted himself as a wholesome American boy: a football player who spent most nights working out with friends, dutifully recording his activities in a calendar, like his father had.

But acquaintances have come forward to tell a different story. “I can unequivocally say that in denying the possibility that he ever blacked out from drinking, and in downplaying the degree and frequency of his drinking, Brett has not told the truth,” a Yale classmate, Chad Ludington, told CNN on Sunday. Entries in Kavanaugh’s high school yearbooks and letters between his friends also suggest he had a more debaucherous past than he let on.

The judge’s real drinking habits matter not only because he may have lied under oath about them but because some are speculating that he may have done things — including assault women, such as Christine Blasey Ford — while he was too drunk to remember it. And the science of blackout drinking reveals that’s a real possibility. Here’s why.

Blackout drunk doesn’t mean you passed out. It’s a type of amnesia.

During the proceedings on Thursday, Kavanaugh seemed to confuse blackout drinking and passing out. In a line of questioning about how much heavy drinking he engaged in during his youth, Rachel Mitchell, the prosecutor hired by Republicans to question Ford and Kavanaugh on their behalf, asked whether he’d ever passed out from too much booze. He answered: “I’ve gone to sleep, but — but I’ve never blacked out. That’s the — that’s the — the allegation, and that — that — that’s wrong.”

The exchange belies the most common misunderstanding about blackout drinking, according to Sarah Hepola, author of the book Blackout: Remembering the Things I Drank to Forget. Blacking out doesn’t mean drinking to the point of involuntarily falling asleep, as Kavanaugh suggested, she told me. Instead, it’s a form of temporary, alcohol-induced amnesia.

“Blackout is a condition in which you are still walking and talking and interacting with people, but the part of your brain that places memories into long-term storage has been disabled by the heavy drinking,” Hepola said. “So you are not recording these memories.”

That part of the brain — the hippocampus — is key to helping people form new memories, and alcohol affects it both directly and indirectly by interfering with its memory storage function and messing up the interactions between the hippocampus and other brain regions. Once a person is sober again, the brain’s memory processing returns to normal.

But not everyone who drinks to excess blacks out. “Only half of people have [blackouts] and there’s a genetic link,” Hepola said.

Similarly, there’s no single alcohol threshold that causes blackouts. The American Addiction Centers says blacking out becomes more common after a person’s blood alcohol level reaches 0.15 — the equivalent of four to six units of alcohol, consumed in rapid succession.

But the point at which alcohol interferes with memory isn’t the same for everyone, just like it takes different people different amounts of booze to become drunk. As a general rule, though, the more a person drinks, the more likely they are to experience blackouts. And blacking out from drinking isn’t all that uncommon. In surveys of young adults, between 20 percent and half of those who ever drank reported a recent blackout experience.

People often don’t know they’ve blacked out

If you are among the afflicted, you may not even know.

That’s in part because there are two types of blackouts: fragmentary and en bloc. Here’s Aaron White, a senior scientific adviser at the National Institute of Alcohol Abuse and Alcoholism, explaining the difference:

En bloc blackouts are stretches of time for which the person has no memory whatsoever. Fragmentary blackouts are episodes for which the drinker’s memory is spotty, with “islands” of memory providing some insight into what transpired, and for which more recall usually is possible if the drinker is cued by others. Blackouts are much more common among social drinkers than previously assumed and should be viewed as a potential consequence of acute intoxication regardless of age or whether one is clinically dependent upon alcohol.

So blacking out doesn’t necessarily involve waking up the next day after drinking and having no idea what you did last night; it can mean you can’t recall a few details or some small segment of your evening, which is why you may not realize you had a blackout.

In the three years since Hepola published her book, she says she gets messages every day from people saying they didn’t know they were having blackouts. Until she quit drinking, she didn’t realize how much they played a role in her own actions when she was drunk. She’d pour beer on other people, take off her clothes — behaviors that weren’t consistent with her self-perception.

“It’s very common to do something in a blackout and to say something you did in a blackout was not you — because sober, integrated you isn’t that person,” Hepola explained. “Blackout drinkers experience it as a Dr. Jekyll/Mr. Hyde experience.”

Being blackout drunk is associated with risky behavior and getting into trouble with the police

Equally disturbing: You may not know that someone else is in a blackout. “As a general rule, you can’t tell if someone else is in a blackout because you can’t know what’s going on in their mind,” Hepola said. They may act just as if they were intoxicated and processing memory normally.

But there are a few signs to look out for — even if they aren’t foolproof evidence of a blackout. The person might seem easily distracted, repeat themselves often, and appear “unconcerned about the thoughts or feelings of those around them,” the American Addiction Centers says.

During blackouts, people are also at an increased risk of injury — and may be more likely to engage in risky behaviors that aren’t in line with their sober personalities. According to White, when researchers interviewed 50 undergraduate students about their blackout experiences, they found that “students reported engaging in a range of risky behaviors during blackouts, including sexual activity with both acquaintances and strangers, vandalism, getting into arguments and fights, and others.” Researchers have also found that getting into trouble with the police, arguing with friends, and doing something you regret are associated with blackout drinking.

So, again, that’s why the question of Kavanaugh’s drinking behavior matters — though it seems the only true answers to the question of whether he’s ever blacked out while drinking can only be “I don’t know” or “I have.”