Around here in the autumn crows engage with various nuts, hard shell ones included difficult or impossible for them to open. So they frequent the bicycle tracks with high traffic, fly above you from the back, elevate a bit while dropping their nuts so you can run those over. Lots of heavy cargo bikes are used by families here, so it is a fruitful exercise for them. Assuming the cyclist realises what is happening and instead of avoiding the nut - like I did the first time not having a clue what this is about - run over it.