Any enemy that normally bounces and stays in the level when thrown (e.g. Shy Guys, Tweeters, Snifits) will fall through the ground instead while you're shrinking from taking damage or growing from touching a heart. You'll have to throw the enemy first, then quickly trigger a size change while the enemy is upside-down. If the ground is thick, there's a good chance that the enemy will end up stuck inside the ground.

See trapped in Fryguy's room for another glitch caused by changing sizes.