Brain
Brain, intellect, mental capacity, brainpower, wit, powers of comprehension, understanding, judgement, mentality, head, subconscious, ego, brainbox, loaf, kop, sanity, mental faculties, reason, marbles, intelligence, intellectual capabilities, brains, wits, powers of reasoning, powers of thought, reasoning, sense, perception, imagination, psyche, grey matter, brain cells, smarts, ratiocination, mental balance, senses, and rationality.
3. opinion
Opinion, outlook, view, point of view, judgement, feeling, persuasion, way of thinking, attitude, viewpoint, belief, thoughts, and sentiment.
Intellect
Attention
Attention, concentration, attentiveness, thoughts, and thinking.
Remember to
Be/make sure (that), take care that, be/make sure to, take care to, see (that), remember to, and don't forget to.
Be careful of
Be careful of, look out for, take care with, be cautious of, be watchful of, take care, watch out, beware, be wary, keep one's eyes open, watch out for, beware of, be on one's guard for, be wary of, keep one's eyes open for, be careful, look out, be on one's guard, be watchful, and be cautious.
Pay attention to
Pay attention to, heed, attend to, be heedful of, mark, listen to, have regard for, be mindful of, follow, adhere to, take heed of, pay heed to, take note/notice of, note, concentrate on, observe, respect, obey, comply with, and regard.
Look after
Look after, keep an eye on, care for, watch, guard, take care of, attend to, tend, have/take charge of, and protect.