I have never fully understood what to click on.

In the grid captchas, when it asks one to click on the motorcycle, do you click every box that has even a small portion of the bike?

Do you click on boxes that include the rider?

Whoever developed them seems to believe they are intuitive but I would disagree. 

 What about the moped? That's what always annoyed me 

 Amen!!!

Is it a motorcycle?

My opinion is no.