Certain ranged attacks involve shooting multiple projectiles at once, but it's still a single attack. So what if you are shot by, say, Manyshot, or that one monster from the ELH who can throw 50 boulders as a single attack (discounting the fact that "unusually massive" attacks can't be caught this way: imagine being Enlarged in this particular case), can you catch all the projectiles? Snatch Arrows is derived from Deflect Arrows, which reads:
Once per round when you would normally be hit with a ranged weapon, you may deflect it so that you take no damage from it.
So are you stuck with catching just one projectile, or can you end up with a fist full of arrows?