Definition of no brainer
"No brainer" is an English expression that is difficult to translate word for word. Literally it would be "no brain" or "without the brain". More logically, "no brainer" could be translated as "game to do without the need to think". If someone pushes all in and you have aces in hand, it's a "no brainer" call. No need to analyze anything, the play is so obvious, it's a "no brainer". You can also say "this player bluffs so often on the river, that it's a no brainer call" or "this player folds so often on the river, that it's a no brainer bluff". A game that doesn't deserve any thought.
Take your time, even for the no brainer
Obviously, some poker games are no-brainers, but in order not to give away any information to your opponent, it's a good idea to always play at the same pace. Whether the situation is difficult or easy, you should always take a few seconds before making your move. This has at least two advantages. First, it ensures that you have seen the situation, that you have a full hand before you make your "no brainer call". Two, it allows us to not give information to our opponents, otherwise they might end up thinking that if you play fast, you are strong and if you play slow, you are weak.