The male platypus has a venomous spur.
Why it is true
The venom is used in fights and is painful to humans.
Source: Mammalogy
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.