Given the following context:

The cartoon opens with a live action sequence of Cab Calloway and his orchestra performing an instrumental rendition of "St. James Infirmary". Then Betty Boop gets into a fight with her strict, Yiddish speaking, Jewish parents, and as a result, runs away from home with her boyfriend Bimbo, and sings excerpts of the Harry Von Tilzer song "They Always Pick on Me" (1911) and the song "Mean to Me" (1929).
Betty and Bimbo end up in a cave with a walrus, which has Cab Calloway's voice, who sings "Minnie the Moocher" and dances to the melancholy song. Calloway is joined in the performance by various ghosts, goblins, skeletons, and other frightening things. Betty and Bimbo are subjected to skeletons drinking at a bar; ghost prisoners sitting in electric chairs; a cat with empty eye-sockets feeding her equally empty-eyed kittens; and so on. Betty and Bimbo both change their minds about running away and rush back home with every ghost right behind them. Betty makes it safely back to her home and hides under the blankets of her bed. As she shakes in terror, the note she earlier wrote to her parents tears, leaving "Home Sweet Home" on it. The film ends with Calloway performing the instrumental "Vine Street Blues".

answer the following question:

Who sings "Minnie the Moocher"? 

a walrus