Procs (lambdas, procs and Proc-wrapped blocks) and Methods are callable and all respond to #call.

As wycats pointed out in a post earlier this year (http://yehudakatz.com/2010/02/21/ruby-is-not-a-callable-orie...), the reason you don't need to explicitly call #call on methods is that Ruby is designed for the common case of calling methods. In addition, it's uncommon to even explicitly use #call or #[] on Procs since calling them is built into the language via yield.