"First, he pointed that giant metal rod at me and out came a glass vial, it exploded next to me! Next thing you know, out comes a friggin’ bear! Then, as if that wasn’t bad enough, he sticks it in the ground. It expands and he walks into it to get a snack!" - Xzud, Experimental Arms Dealer.
Another real world thing. White tea. Can only be picked two days a year, the two days before the flowers blossom. Could be a similiar plant that...is the deadliest poison known, cure known diseases or psychosis, or a potent herb that just tastes awesome.