Sometimes the bus/boat/truck has motorbikes sometimes bicycles. Is that a petrol-powered bicycle, or a motorbike to the [USAmerican?] person who wrote the rules!? Are all large yellow vehicles buses in USA or do you have minibuses, oh wait, are minibuses buses.

I've worked out fire engines are trucks for captchas, not sure about Transit-type vehicles, lorries are trucks apparently but goods trucks on railways are not trucks!

Is a traffic light only the lens/led array or the black light-holder too? Do pedestrian lights count as traffic lights? Are those weird lights hanging in the middle of junctions 'traffic lights'.

Wish they'd just tell you what counts.

I have noticed that times I realise after clicking that I missed a square they tend to go through whilst many times I get repeated captchas when I know I got it right. Success, as a user, seems impossible to predict.