Throw Your Voice

Bart read the book so he could "[add] a new trick to [his] pranking repertoire".  He interrupted his reading, however, to go Christmas-caroling with Milhouse and Lisa, being won over by Lisa's telling him that the people whose houses they caroled would give them cookies.  Unfortunately, the trio had a run-in with the school bullies Dolph, Jimbo and Kearney, who wanted all the free treats to themselves.  The encounter resulted in Lisa being buried up to her neck in a pile of snow, Bart being stuffed head-first into a garbage can, and Milhouse being hung from a mailbox by his underwear. 

After the trio freed themselves, Bart used his newly-acquired ventriloquism skills to take revenge.  During the encounter with the bullies, Bart had told Jimbo that the free treats were coming from Moe.  The caroling trio went to Moe's house, where they arrived and hid behind a hedge just as the bullies were singing "Silver Bells" for Moe.  Bart then threw his voice, making it sound like the bullies were singing "This is to make up for all the prank phone calls during the year!"  At this revelation, Moe became angry, threatened the bullies and brandished a meat cleaver at them, scaring them out of the neighborhood.  With the bullies gone, Bart, Lisa and Milhouse resumed their caroling.