It's well known they can carry grudges, but one day, as I was walking down the sidewalk, a pretty sizable rock smacked the pavement next to me, seemingly out of nowhere. If it had hit my head I would have been hurt. I finally look up and see a big crow staring directly down at me - it had dropped it from the power lines, it had seemingly been intentional, maybe as a warning, I don't know. I attributed it to malice towards the vagrants that harass them.

I was amazed at how much intelligence it would take to 1) form a grudge 2) form intent to threaten/harm, 3) formulate a plan using a weapon with cause -> effect to execute intent, 4) wait for opportunity.

I have observed a lot of very intelligent behaviors from these birds but that was the wildest one. I have seen it happen once since, so I'm convinced it isn't an accident.

Birds have higher neural density than mammals (https://www.pnas.org/doi/10.1073/pnas.1517131113) so can pack a lot into their tiny heads. I do wonder what they'd have to say, if given the chance.