but riddles should only have one possible answer.
Good point. There can be riddles that have different answers. What I meant was when you have a riddle with only one answer, it should only be possible to get that answer. If you are going to say "no" to an answer that technically would work simply because it wasn't the one you had in mind, then you intended there to be only one answer. To accomplish this, you add the extra information specifying what you can and can't do. Other than that, I thought this was a neat riddle. With that extra information this riddle would have been a lot of fun to work out.