As we all know,Ruby Blocks and Ruby Methods work in tandem and the output/value of the last line/expression being executed by the block is returned to the associated method .

Have a look at this example:

2.1.5 :006 > def demo
2.1.5 :007?>   puts yield
2.1.5 :008?>   end
 => :demo 
2.1.5 :009 > demo { "hello!"}
hello!
 => nil

here,the yield keyword within the method finds and invokes the block the method is called with and the block returns a string object namely "hello" and method simply prints it.

Now,coming to the inherent subtleties of using return keyword within the body of  a Ruby block ,the use of return keyword isn't recommendable because instead of returning from the block itself ,it returns from the method where the block is being defined .

Have a look at this below given example:

def first_method
  puts yield
end

def second_method
  first_method { "hello"}
end

second_method

When we call second_method  it prints hello.

Now a slight change in code:

def first_method
  puts yield
end

def second_method
  first_method { return "hello"}
end

second_method

now,it won't print anything because the return keyword instead of returning the last expression executed ,returns from the body of second_method where the block is being defined.

So at last for recapitulation ,we can pass parameters to a block or use the return value from the block or both or neither.For example ,the each  method simply ignores the return value from its blocks.

Thanks for Reading.