Half of all children aged three to 10 and 5 percent of adults get chatty in their sleep. But what do they talk about? A team of French scientists set out to find out in one of the largest studies on sleep talking to date. Their results have been published in the journal Sleep.

The group tracked the speech of 232 adults over several nights, then analyzed the recordings to calculate the number of words, propositions and speech episodes, frequency, gaps and pauses, lemmatization, verbosity, and tone of voice during periods of sleep talking. In all, there were 882 speech episodes over the course of the experiment.

So what did they find? Well, people aren't spilling their deepest, darkest secrets when they're out cold. In fact, the sleepers in the study were only intelligible 41 percent of the time. The remaining 59 percent of noises were a random mix of mumbles, shouts, whispers, laughs, and other non-verbal sounds. 

It also turns out that people can be very aggressive in their sleep. Researchers noted that polite words were used in only 12 of the 361 episodes during which comprehensible speech was detected. In contrast, almost 10 percent of clauses recorded contained profanities. Not totally unsurprisingly, male sleepers were more likely to swear than female sleepers. But then again, they also tended to be more vocal overall than the women in the study.

The French equivalent of the F-bomb was the group's favorite curse word, says The Times. It was tracked in participants during sleep at a rate roughly 800 times higher than during waking hours. 

Another word the sleepers seemed to like a lot was "no". It was the most frequently recorded word. 

Maybe this is because people are more confrontational in their sleep. Researchers found interrogation-type scenarios accounted for 26 percent of speech episodes. They suggest that this could be because sleep talking is the "punchline" of a conversation, ie the most aggressive point of the speech, reports The Times. This would help explain the overwhelmingly disproportionate use of negative language. 

And while the participants may have been a touch grouchy in their sleep, at least they were grammatically correct. According to the researchers' observations, they adhered to typical adult speech patterns – putting to bed the theory that people who talk in their sleep tune into a childlike state.

So there you have it. Sleep talkers don't have to worry about accidentally revealing too many secrets but they might not make the most agreeable sleeping partners.