I followed these instructions: http://codex.wordpress.org/Pages#Creating_Your_Own_Page_Templates
My understanding of those instructions was that the file snarfer.php needed to be in the folder 'themes', so it appears in the same list as the following folders and file:
twentyeleven (folder) twentyeleven-child (folder) twentyten (folder) index.php
…but when I put it there, and went to create a Page, the new template didn't appear as an option in the list Default Template / Showcase Template / Sidebar Template.
So I tried putting snarfer.php in the folder 'twentyeleven-child' -- which is the active theme.
And the new template now appears in the Template list when I create a Page.
Do I have snarfer.php in the right place?