When you type “congratulations” or “congrats”, iMessage (iOS 11 is the first time I noticed this) automatically sends that confetti animation whether you want it or not. Same goes with the balloon animation when you type “happy birthday”. (Don’t know if any other specific phrases but there may be more)
How do you turn off these auto animations? I’m not talking about the manual feature of sending animations. I know about that. This is done automatically without prompting when you type the magic words.