Originally Posted by alakazam^
You can try paying attention to the sounds. A violent patch sounds louder than a normal one and it also looks like the grass grows a bit and shakes on top of the surrounding patches. The normal one shakes but stays mostly in place.
On this topic, probably a silly question but is there any way to differentiate between a rare patch with the Pokemon you're chaining and a rare patch with a different Pokemon? That's exactly what was messing me up when I was trying to chain Scatterbug - I'd see a patch that shook a lot more than the others and looked exactly like the ones I was aiming for, I'd walk into it, and then I'd get a Weedle. I'm assuming that's because Weedle are just as rare as Scatterbug, but...in that case, I don't know how the heck I'm supposed to chain one Pokemon without getting interrupted all the time. xD

Also, following up from my previous post, I have been trying chain fishing without any success. That's understandable, since my longest chain is probably about 10, although I haven't checked with the guy at the house on Route 16 yet. Usually I end up breaking the chain by reeling in too slow, which is kind of dubious to me because several times I was sure that I pressed A quickly enough...but apparently I didn't. xD