Module Eval Syntax

[John W. Long]

class MyModule; end
=> nil

MyModule.class_variables => []
MyModule.module_eval do ?> @@test = true
end => true
@@test => true
MyModule.module_eval "@@weird = true" => true
@@weird

NameError: uninitialized class variable @@weird in Object
from (irb):8

MyModule.class_variables => ["@@weird", "@@test"]
Object.class_variables

=> ["@@test"]

What in the world is going on here? Why does the block syntax eval
differently than the string syntax? And why does @@test get defined on
both MyModule and Object?