I'm convinced hitting a baseball is the single most difficult thing in sports. Hitting a pitch moving that fast -- a 90 mph fastball travels 60-feet, 6-inches in 0.46 seconds -- totally amazes me. Nevermind doing it when the pitch breaks or when there are 50,000 screaming fans in your ear.
As amazing as hitting a baseball is, I think it's even more amazing (some) hitters are actually able to read the seams on the baseball as it hurls towards them, then use that information to decipher exactly what type of pitch is on the way. That blows my mind. The human brain, man.
Here's a really neat graphic showing what different types of pitches look like as they approach the plate. Different pitches have different spins, so the seams create a distinct visual for each pitch. Check it out:
I've heard of hitters looking for the red dot on a slider. Other than that, it would all be a blur to me.