The subway is definitely not the kind of place where you just want to curl up and get comfy on the floor. Add a rat to the equation and you just went to the next level of nastiness. Hopefully you won't ever have to apply any of this knowledge, but in the event that you find yourself in a similar situation, here are a couple of options on how to handle it.
You can just play it cool like these peeps and act like it's NBD (Note: Not for the faint-hearted)
If you don't have nerves of steel, don't worry--you still have options. For example, you can just play your fear off like "oh, there's a rat, I didn't even notice...I just always sit like this"
You could just own your horror and get the hell out of that nasty vermin's path
Or you could leave yourself with some options, like the guy who won't commit to the floor OR the bench
Or, in case there happens to be a sports agent on the subway, you can use it to show off your mad skillz