Different Bubble Pops.
Bubble Pops are objects in Yoshi's Story that Yoshi can hit with an egg by pressing the Z button on the Nintendo 64 controller. When Yoshi does this, the Bubble Pop will explode, releasing the item inside of it. The player can see the item before popping it, as the Bubble Pops are transparent. When touching the Bubble Pop, the Bubble Pop will simply move in the direction Yoshi touched it in, making a "boing" sound while doing so. If your Yoshi touches it six times, the Bubble Pop will explode.
Bubble Pops mostly contain fruit, although sometimes they contain Surprise Balls, that can release a Shy Guy, a Heart Fruit, fruit on a parachute, or Walking Heart Coins. The player cannot see what is inside a Surprise Ball.