This happened so, so much to me when I was little. The worst ever was when I was around 13-14 and I really wanted to keep fish again. I was checking out aquarium books at the library, drawing fish, begging to go visit the pet store to look at fish, just... talking about fish all. the. time. Christmas was coming up so yeah! Perfect opportunity to ask for fish for Christmas.
So you know on the days nearing, you get to look at/shake the presents under the tree, try to guess what you got. Medium sized, rectangular, triple-wrapped, kind of like a miniature pillow, THIS BAG... WAS VERY SQUISHY (and wait, not water squishy). Felt like many, tiny, loose bits 'n pieces inside. "Rocks. This is aquarium rocks!!" I was so excited and happy, this bag was the clue that I was getting fish!!
Christmas day, opening gifts like mad, I hone in on the bag of rocks and rip into it, glee, already smiling, SO HAPPY! I'm getting fish!! I'm getting... seed? Birdseed? Oh yeah, I've got two pet parakeets. It was birdseed for my bird. ;o;