Booting Mountain Lion - OS screen?

Hi all - I recently upgraded my iMac from Snow Leopard to Mountain Lion. When I power up now, I get a screen I didn't get before - it looks like a Unix shell/OS screen. I have to type 'exit' at the prompt to boot Mt. Lion. Is this normal? I don't think it did this the first time, but for some reason it does now. It never did this when I was running Snow Leopard.

here is a crappy shot of what the screen looks like.

Everything runs fine once I get past this. I am just wondering why I get this and what it means.

Thanks.