Definition of no brainer
"No brainer" is an English expression that is difficult to translate word for word. Literally it would give "no brain" or "without the brain". More logically, "no brainer" could be translated as "game to be done without thinking". If someone pushes all in and you have the aces, it's an call "no brainer". No need to analyze anything, the game is so obvious, it's a "no brainer". You could also say "that player bluffs so often on the river, that it's an call "no brainer"" or "that player lies down so often on the river, that it's a no brainer bluff". A game not worth thinking about.
Take your time, even for the no brainer
Of course, some poker games are no brainer's, but in order to avoid giving information to your opponents, it is good to always play with the same rhythm. Whether the situation is difficult or easy, you should always take a few seconds before making your move. This has at least two advantages. One, you make sure that you have seen the situation, you make sure that you have your hand full before making 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're strong and if you play slow, you're weak.