And their venom HURTS. They’re not particularly deadly or anything but their venom will land you in the hospital or at least laid up in bed for a while. My stepmother grew up out in the bush in NSW the ‘70s and received one of the few recorded platypus envenomations and she described it as the most painful experience of her life. She said childbirth was a breeze compared to the platypus sting!
We were taught a similar trick in physics - point your right-hand thumb in the direction that current (or electrons, same same) is travelling and the curling of your fingers shows the direction of the resultant magnetic field that the current creates.