In Level 10 (Rat Race), when you kick the bomb in any of the three "races", the Spazz you've been racing will generally fall down from the top of the screen and hit its head on the girder, sending you to the next segment. You still can hit Spazz in this short while with regular or double-tap charge attacks as usual; if you're able to hit the rat with a Final Smash move before you fall to the next segment, the level-finish music will play and you'll be warped to Level 11.