A word of caution on the aspirin...
Make sure you use the type that come in the small sealed cellophane bag-- because if you just glue a couple aspirin to a sheet of paper-- just watch the reaction your letters will cause after they reach their destination. This is of course AFTER the letters have gone through the post office machinery and the aspirin has been ground into a fine powder.
Don't even ask! Or I'll have to tell you stories about the FBI and National Disease Control!
