If you are told that you are in that situation, then you would assign a probability of 50⁄51 of being behind a blue door, and a 1⁄51 probability of being behind a red door, because you would not assign any probability to the possibility of being one of the cats. So you will not give a probability of .99 in this case.
If you are told that you are in that situation, then you would assign a probability of 50⁄51 of being behind a blue door, and a 1⁄51 probability of being behind a red door, because you would not assign any probability to the possibility of being one of the cats. So you will not give a probability of .99 in this case.
Fixed, thanks. (I didn’t notice at first that I quoted the .99 number.)