Duck Says Moo

Spencer was playing with their little Leap Frog radio thing and he happened upon some of the songs. At one point the tune of Old McDonald started.

Us: Spencer, what animal is on the farm?
Spencer: Cow!
Us: What sound does a cow make?
Spencer: Mooo
Us: Not overly impressed. I mean, he knows this stuff. Moving on. Spencer, what other animals are on the farm?
Spencer: Duck!
Us: And what sound does a duck make?
Spencer: Mooo!
Us: Hmm, let's refresh. What sound does a cow make?
Spencer: Mooo!
Us: If a cow says moo how can the duck say moo too?
Spencer: Because the duck is inside the cow's tummy!

Makes perfect sense now!