$ od -c
[Hit left arrow]
^[[D
0000000 033   [   D  \n
0000004

$ od -c
[Hit right arrow]
^[[C
0000000 033   [   C  \n
000000

expect.test script:
#!/usr/bin/expect -f
spawn /bin/bash
interact {
  "\033\[C"             {exp_send "\033\[C";
                         send_user "Right Arrow Pressed\n"} # Right Arrow
  "\033\[D"             {exp_send "\033\[D";
                         send_user "Left Arrow Pressed\n"} # Left Arrow
}

Running the script:
$ ./expect.test
spawn /bin/bash
$
[Hit right arrow]
Right Arrow Pressed
[Hit left arrow... no output but the key does work and moves the cursor]