The difference between the sheep and the goats

The other day, Marilyn was singing "Old MacDonald Had a Farm" with Lily and one of the animal sounds she made was a sheep--"baa baa".  The song went on and on, and pretty soon 'Old MacDonald' had a goat.  Marilyn was stumped.  What sound does a goat make?  I chimed in with 'baa baa', just like I had with the sheep.  Marilyn corrected me and said, "That's what the sheep says!  What do goats say?"  I said, "There is no difference!", and laughed. You see, I was so sure that goats and sheep are the same animal that I told Marilyn as much with all the authority I could muster.
  
Then today, I was reading Exodus (12:1-8, 11-14) where the Lord tells Moses and Aaron how to celebrate the Passover feast; "The lamb must be a year-old male and without blemish. You may take it from either the sheep or the goats."  What?  They aren't the same?  They can't be, if our Lord tells us there is a difference.  Why didn't I catch this before?  I've heard the Scripture verses about sheep and goats my entire life, but for some reason the difference just didn't "click".  At worst, I thought that goats were simply "black sheep", since their fate is not as good as the 'sheep' of the Good Shepherd.

Thank God for the Internet.  I 'googled' "the difference between sheep and goats" and found out more than I needed to.  One of the sites I visited gave me the most basic difference--(tongue in cheek)--sheep say, "baa baa" while goats say, "maa maa".

How's THAT for theology?