Each with index doesnt work

application.controller.js

import Ember from 'ember';

export default Ember.Controller.extend({
  appName: 'Ember Twiddle',
  arrayOfStrings: ['Jon', 'Rob'],
  secondArrayOfStrings: ['Snow', 'Starc']
});

application.template.hbs

<h1>Welcome to {{appName}}</h1>
<br>
<h2>Index doesnt work:</h2>
{{#each arrayOfStrings as |str index|}}
  <p>{{index}}: {{str}} {{secondArrayOfStrings.[index]}}</p>
{{/each}}

<h2>Zero does work:</h2>
{{#each arrayOfStrings as |str index|}}
  <p>{{str}} {{secondArrayOfStrings.[0]}}</p>
{{/each}}
<br>
{{outlet}}
<br>
<br>

twiddle.json

{
  "version": "0.6.4",
  "EmberENV": {
    "FEATURES": {}
  },
  "options": {
    "enable-testing": false
  },
  "dependencies": {
    "jquery": "https://cdnjs.cloudflare.com/ajax/libs/jquery/1.11.3/jquery.js",
    "ember": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/2.4.1/ember.debug.js",
    "ember-data": "https://cdnjs.cloudflare.com/ajax/libs/ember-data.js/2.4.0/ember-data.js",
    "ember-template-compiler": "https://cdnjs.cloudflare.com/ajax/libs/ember.js/2.4.1/ember-template-compiler.js"
  }
}