Hidden two big hearts

In level 3-2 there is a boulder over some quicksand. Shoot the boulder until it is destroyed. Then fall through the quicksand. Instead of dying, you will end up in a secret area with some good bonuses. You'll still have to fight and jump plenty (over holes this time instead of cacti), but you had to do that above ground as well. Down here, however, you will be rewarded with 2 big hearts if you find them in their boxes. When you find these, Fievel becomes capable of taking 5 hits instead of the usual 3.