user_query: add sausage to my grocery list
response_text: Sure, I added sausage.
user_query: scratch that add tomatoes to my grocery list instead
response_text: I couldn't find that item on your list called "grocery."
user_query: add it
response_text: What do you want to add?
User: tomatoes
Parse: Add_item_to_list ( items « tomatoes » )