HTTP and Hidden Fields

I am not exactly sure how to search if this has been asked, but I am curious if there is a way I can pass HTTP data to the form, like…

“http://mywordpress.com/form7?Data=Dog”
and have it put “Dog” in a hidden field to be emailed to me. Which raises the second question of whether it’s possible to HAVE hidden fields.

Thank you.

http://ww.wp.xz.cn/plugins/contact-form-7/