Having a split-screener does nothing other than give you an extra player to help. I was split screening when I did the Easter Egg. I'm assuming you failed and had to restart. Remember Avo isn't released until you turn on the power. I've also heard he only shows up at the beginning of a new round, you if you were babysitting a zombie so the round counter doesn't advance, you need to kill him.
http://i152.photobucket.com/albums/s166/Ionizer_1/squirrel.jpg Carrier of Squirrel Flu