surprise.rb

# original code
class Foo
  def foo
    :original
  end
end

# reference made from original code
method = Foo.new.method(:foo)

# monkey patch
class Foo
  def foo
    :patched
  end
end

# Reference gets evaluated
# Effect not visible. I'm surprised.
p method.call # => :original 

I'm not that surprised. Similar to what alias does

# original code
class Foo
  def foo
    :original
  end
  alias bar foo
end

# monkey patch
class Foo
  def foo
    :patched
  end
end

p Foo.new.bar # => :original

Which is also an interesting caveat, especially when providing "convenience" aliases for a "humane" interface.