Was it excellent intuition, psychic abilities, or simple observation that saved Gus Fring from Walt's car bomb in Breaking Bad season 4? At first, the partnership between Walter White and Gustavo Fring was a fruitful one for both parties. Walt had the method to make high-quality meth and Gus had the infrastructure to manufacture and distribute. Interestingly, both men also shared a cold, business-like pragmatism. Of course, Walt and Gus were bound to clash eventually. In Breaking Bad's fourth season, conflicting morals and diverging interests sour their relationship so badly, Walt is left waiting alone in a darkened house for Gus' assassins to come.
Recognizing Gus has now become a threat, Walt spends almost the entirety of Breaking Bad season 4 trying to kill the chicken man, and hits a new low by poisoning young Brock with ricin, hoping Jesse will be convinced that Gus is responsible. With Jesse distraught, Gus visits the hospital personally to order Jesse back to work, and it's here that Walt sets up an assassination attempt. While Gus is inside the building, Walt rigs his vehicle with explosives and retreats to watch the fireworks. After speaking with Jesse, Gus heads back towards his car, but suddenly realizes something is amiss and walks away, presumably taking a very tense bus ride home with his lackeys. Breaking Bad never reveals what tipped Gus off, so how did he know about the car bomb?
Some have speculated that Walt gives himself away thanks to his glasses. Breaking Bad fans know all too well that no detail is included without reason, and when Walt is watching Gus's rigged car from afar, his glasses are curiously perched on top of his head. It's possible that the glint of sunlight from these spectacles gives away Walt's hiding place, signaling to Gus that treachery is afoot. Fring is nothing is not observant, and cautious enough to be deterred by a simple errant reflection off a glasses lens. Perhaps if Walt had removed himself from the area entirely, Fring would have fallen for the trap.
More likely, however, is that receiving news of Brock's poisoning started the gears turning in Gus' brain. When Gus visits Jesse in hospital, he intends to simply coax his star cook back to work. But after discovering that Brock has been been poisoned, and isn't simply "ill," Gus' entire demeanor shifts, and he gives Jesse the rest of the week off. Obviously, Gus knows he didn't poison the child, and is smart enough to single out Walter White as the only other potential suspect. From there, it's a simple deduction for a man of Gus' intellect and foresight: Walt wants Gus dead and poisoned someone Jesse cares about - Walt would've expected Gus to come to the hospital to speak to Jesse, and the car has been left unattended for the entire visit, giving ample opportunity to set a trap.
Gus Fring spends so long standing in the parking lot deliberating that his trepidation is more likely to come from this step-by-step thought process than catching sight of Walt on a nearby building, which surely would've prompted Gus to move quicker. The tense wait also suggests that even after walking away, Gus isn't completely sure his car has been tampered with, merely realizing that Walt had motive, means and opportunity and decides not to take the risk. The scene is certainly ambiguous, however, and this is part of the reason Breaking Bad remains such a fascinating series to dissect. Not explicitly giving away the answer invites the audience into the mind of Gus Fring, leaving fans to guess his thinking in the same manner as Walt himself.