Why can't I bake a cupcake without egg?

I was hungry and kinda boared so I took out a little cup and mixed milk, flour, sugar, vanila, and er. I did not want to break an entire egg for two cupcakes, so, not knowing it's signifficance, I left out the ingriedent. I attempted to stir the concoction but the er was stuck in little lumps. My brother suggested that I should have melted the er so, without thinking, I put the plastic cup in the microwave. When the cup was limp and melted I transfered the mix to a new cup. I esily stirred it, as the er had been melted. I decided that I had worked too hard and overlooked the plastic poison. I placed the concoction into two paper cupcake holds, one sprayed with pam and one without. I placed them into a cupcake tin and into the oven, which I had set to bake at 350 degrees ferinheit. 8 minutes later, which I spent watching my brother use the Pam and a lighter as a flamethrower, I took my 2 cupcakes out of the oven to be unpleasantly surprised to see them