Verified answer

i believe that in some cases, the grass will have the same slightly darker irregularity as in FR and LG, but there isn't a sure-fire way to tell every time. when you're in caves, i suggest checking the seemingly random and really short walkways for items, as there is usually something there. click on rocks, too, as they hide things, at times.

if you don't mind it, you could also just use the item finder, if you get suspicious of any hidden items.