It's best to use `Proc.new` rather than `proc` for code that needs to still work on 1.8.7.  Unfortunately, on 1.8, `proc` acts more like `lambda` than a `Proc` :(  They corrected this on 1.9, but best to avoid it for now.

http://joshcheek.com/blog/1_lambda_proc_and_proc_new#proc-avoid-this-since-its-behaviour-differs-across-commonly-used-versions