When you are designing your conversational interface, even if you have opted to use a menu based interface as your primary method of interaction, it is a good idea to train your bot to recognise a number of key phrases that everyone will use.
Your bot must be able to respond to basic greetings such as "Hi" "Hello" "Hey" "Whatsup". You don't want your customers to be sent to an error message as soon as they start interacting with your bot. As a minimum they should be able to respond with a variety of greetings and then direct your users to the main interface menu.
This means phrases such as "Bye" "Goodbye" and "See you later". You want to leave a good impression once your customer has finished using the bot, and if their experience has been good they will usually look to close the conversation as they would with any normal human being. Your bot should be able to respond to your customer in the same way.
As with the parting words, often if your bot has managed to help your customer they will send words of thanks, just as if they were speaking to a real human being. So your bot needs to be able to respond to "Thanks" "Thank you" "Cheers" and the like.
So if your users get stuck, and some of them will as bots are still an emerging technology for most people, you need to be able to help them. If someone types "Help" "Help me" or "I'm stuck" your bot should be able to give assistance. As a minimum, by diverting your customer back to the main menu, but preferable should be giving them some guidance on how to interact with your bot effectively. Most of, if not all, chatbots include an onboarding sequence which explains to the users the functionalities, what they can ask and the commands that they should use. But because most people are impatient to get started they will skip this sequence, so your bot needs to be able to help them out when they ask for it. Even if you prepare the best onboarding sequence ever, you will need an answer to this question.
So, you've built your new chatbot, tested it and trained it to recognise some key parts of a normal conversation, unfortunately people don't always behave the way you expect. Hopefully most people will work within the planned framework of the bot, but every now and then they will ask questions, or send phrases you might not have planned for. However, most people throw the same curve balls to try to flummox your bot.
For some reason people seem determined to have a love affair with chatbots, a lot of users will profess their love for your chatbot or even ask it to marry them, you need to set your chatbot up to prepare for this, its a perfect opportunity to entertain your users.
People will always question the nature of your bots existence, in fact it is the number one question they will ask your bot. Questions such as "Who are you?" "Are you real?" "Are you human or bot?". Again another opportunity to entertain your users, but best to be up front about the bot being a bot, don't try to fool your users. People aren't stupid and once your users figure out your chatbot is in fact a bot, this could cause problems with brand trust. Your bot isn't ready to pass a Turing test just yet.
Tickle My Ribs
Most people are still treating chatbots like a bit of game, they're still a novelty and a common request is to be told a joke, so make sure you have a supply ready for them, and try to be original, this is an opportunity to impress.
How Are You?
Your bot is going to be asked this all the time, and you can have fun with the answer. This is an opportunity to really let your bots personality shine through. You can train your bot to give interesting, quirky or original answers that reflect the brand image you want to portray.
This is a tough one, it's really difficult for you to predict current events and may have a negative affect on your brand if your bots answers aren't properly thought through. Best to try and gloss over these kind of questions. So for example people may ask your bot how it feels about political leaders, religion or celebrities. Unless your brand is directly linked to these subjects, best to avoid providing an answer.
Your bot should also be able to deal with emojis, stickers, rude words and abuse. There ill be plenty of opportunities for your chatbot to entertain your users dealing with non core questions.