This joke is backwards

Benny is back and he has stopped coughing, thank goodness. Here is his joke:

Question: What animal goes oom oom? Answer: A cow walking backwards!

To find out more about Benny and Millie's jokey fundraising activities go to the Wheelchair Bedroom for Millie website http://bit.ly/YK4nuA or have a look at their gig on Fiverr.com http://bit.ly/Vw0DBi