How to make form_rest() not display a field with Symfony2?

I've started to use Symfony2 but I've some problems. I wanted to render fields by hand but it doesn't work because my field yet rendered by me is displayed with the form_rest() function too, so I have two same fields.

Here is my code :

<div>
     {{ form_errors(form.contenu) }}
     <textarea id="{{ form.contenu.vars.id }}" name="{{ form.contenu.vars.full_name }}">{{ form.contenu.vars.value }}</textarea>
</div>

And, at the form's end, I must put this :

{{ form_rest(form) }}

But it displays the "contenu" field :(

Do you have an idea of what's the problem ?