Michael has eloquently explained how contrast filters work, not just in this thread, but others. The real power of split grade printing is to take an image and apply different filtration, at different duration, on different parts of the print. That is where most of the gain is. You can achieve this by dodging or burning at two, or more contrast filtration grades.
I sometimes use a Number 1, number 3, and number 5 - all in the same print, to accentuate different parts of it at varying filter grades. My normal approach is to first find a good average contrast with a single filter - where it counts in the image. In your example - the cat. then I work the other parts of the picture with lower and/or higher grade contrast filters. So I might begin with an average exposure at Grade 2, and then burn in selected areas with a Grade 1 and a Grade 4.5. The possibilities are endless.
But to just combine two filters, one on top of the other doesn't release any of the true potential of this fine darkroom printing tool. It merely mimics what a single filter is already doing for us, and then we have to ask, in terms of print quality, what did we really gain? I read above that you gained a bit of understanding of the process, which is great! Now let's build on that and get your portrait to where you think it should be in terms of print quality. Study your print and ponder where you could use more or less density and/or more or less contrast, and then make a plan for how to achieve it by sketching it. Then set out to do what you imagine. That's how I go about things, and not saying you have to do this, but I'd be doing you a gigantic disfavor by not explaining that there is a lot more to be had in terms of print manipulation.