She Knows No?

SO there are many dangers around the New Family house that could harm the Twins Liesel and EJ. Dad, ever so on top of it (not), mitigates the risks by constantly monitoring them and employing "redirection," literally picking them up when they have stumbled upon a forbidden area or thing and giving them something else to focus on by setting them down somewhere else, usually in front of something bright and shiny.

He foresees the limits of this strategy and will get around to properly baby proofing one day, but that is not the point of this post.

Dad has observed that Buggy seems to understand the word "no." That is, when she gets into something that she should not get into, Dad will call her name, gain her attention, say "no," and surprisingly, to him anyway, she modifies her behavior and discontinues the action that earned her the rebuke (Mom is not so impressed because her expectations of her highly intelligent children mean that they should know "no" and several other words by now). It is as if she understands "no" and, more delightfully, has chosen to comply.

She is nine months and a few weeks outta the womb. She knows what "no" means as much as her brother can explain the Cypriot saver's haircut.

But her behavior is uncanny. Dad wonders why she would react to his command as if she actually understood "no." To be sure, he is not complaining. He is judicious in his intervening in his children's activities, restraining himself to only that which is necessary to address imminent harm, and he certainly appreciates the seeming reciprocal respect of prompt and correct response to his "no." However, he would like a plausible explanation.

Mom has a theory. She believes Buggy to be reacting to his tone of voice instead of his actual words. Jake, the late New Family cat was good at this having had a high emotional intelligence. He may not have understood what the Parents said, but he sure knew the meaning of how they said it. A pleasant note meant something good for him (usually a treat or some much wanted affection) while a harsh tone meant someone was displeased with him and he should leave the area immediately. Persuasive as this is, Dad has experimented with several tonal deliveries, some commanding, others pleading, but he still gets the same response. She behaves as if she knows what "no" means. Much like in an earlier experiment, she seems to be reacting to the words he uses as opposed to the way he delivers it.

What could explain it?