title: Iterating through an Array of Arrays returns a different value than expected
body: <pre><code>1.9.3-p286 :039 &gt; (0...x.right.first.chem_species.size).each do |atom|
  1.9.3-p286 :040 &gt;     puts x.right.first.chem_species[atom]
  1.9.3-p286 :041?&gt;   end
  H
  2
  O
  1
   =&gt; 0...2 
  1.9.3-p286 :042 &gt; x.right.first.chem_species[0]
   =&gt; ["H", 2] 
  1.9.3-p286 :043 &gt; 
  </code></pre>
  
  <p>Why doesn't the puts output 
  <code>["H",2]</code> and then <code>["O",1]</code>. (as the second method returns). This doesn't seem right</p>