You’ve completely missed my point with the example of the taste of the beverage being an accident instead of intentional.
Let’s use a mechanism from physics to examine it. Let’s use frame of reference. Look at the case from the frame of reference of the bully. The bully went to school, took a beverage from one of his victims, and found that it tasted nasty. He realizes that the beverage he took could have been poisoned or doctored by the other child in retaliation for the bullying. From there we have two possibilities.
First, he panics, and anxiety causes physical symptoms of headache and nausea. It is an exercise for the reader how much of those symptoms are due to fear or due to guilt. As you say, they are unknowable and thus not relevant to the legality. He goes to the hospital where they run tests and eventually release him the same day.
Second, he schemes, especially when no physical symptoms present themselves. Instead, he realizes he can punish the victim for trying to strike back, while garnering sympathy and getting the rest of the day off. He fakes symptoms, goes to the hospital, they run tests, send him home later that day. It’s a grand adventure and he can continue to milk it for sympathy for days, maybe weeks.
Here is why this exercise highlight why we, as a society CANNOT consider this a crime. The outcome in the frame of reference above, is independent of the actions or intentions of the person accused of a crime. If the change of flavor of the drink was intentional, accidental, or imagined, the outcome is the same.
That all changes if there is explicit communication of a threat. If the victim had told the bully that the drink was poisoned, if the mother had included a note on the drink, etc. etc. NOT just the mom or victim reporting the bullying - there’s nothing explicit to tie the taste of the drink to the reporting. There has to be an explicit message tied to the drink to raise this to assault or harassment.
Finally, here is what makes the comparisons to harassment or stalking so ridiculous. In the US, people are harassed and stalked a lot, with VERY little response from police. In order to get police to pay attention to it, even if there has been frequent, extreme, threatening behavior, there has to be ample, explicit evidence of the behavior. Written or electronic messages, witnesses, video or audio recordings. Even then it’s tough to get law enforcement to put down their donuts and pay attention. But people are insisting that the flavor of a drink is explicit evidence of a threat? Come on. Pull the other one. The fact that the police made an arrest over that is a pretty strong indicator that there is undue influence from the bully’s parents on police to do so.
ETA: Regarding any of this being unknowable until it’s put in front of a jury, that’s nonsense. It is the responsibility (albeit rarely exercised) of the police to only arrest someone when there is evidence of a crime. It is the responsibility of the prosecutor to only charge someone with a crime when there is strong evidence that person committed the crime. Investigation to find that evidence in the US justice system must precede charging someone. [insert Duh-DUH here] If every case where there MAY have been a crime went to trial, our courts would be flooded. It is explicitly the job of police and prosecutors to determine there is a crime and to find evidence tying the accused to the crime. The water bottle and bully’s symptoms would be sufficient to determine there may have been a crime. The missing piece is intent to harm or threaten. Unless they have that, they should hot have charged the mom with a crime. And that is explicitly their responsibility, not to explore whether maybe it was intentional in court.