This is such a fun project! It seems that the model is a bit confused about $_, which I find pretty interesting:

  simedw@laptop:~$ pwd
  /home/simedw
  simedw@laptop:~$ mkdir -p foo/bar/baz
  simedw@laptop:~$ cd $_  
  cd foo  
  simedw@laptop:~/foo$ cd baz
  simedw@laptop:~/foo/bar$ pwd  
  /home/simedw/foo/bar
  simedw@laptop:~/foo/bar$ cd baz 
  simedw@laptop:~/foo/bar/baz$