What's this secura all about?

In my English classes we sometimes unscrambled words while we were waiting for some students to finish a test or assignment. One day a boy brought SECURA to my desk. He was smiling. (I didn't realize at the time that it was a smug smile.) With confidence and experience, I started to rearrange the letters. No result.

''Are you sure,'' I asked, ''that you have spelled it correctly?'' He assured me that the letters were accurate.

''With what letter does it start?''

He shook his head.

That evening I systematically arranged and rearranged the letters until victory was secure. With a sigh of relief, I was amused at the time it had taken.

Editor's note: The answer begins with ''s'' and ends with ''r.''