What does the doggie say?

One of my favorite things Luke does right now is when we ask him what the doggie says, he scrunches his face up and tries to say what the doggie says...only it comes out his own original version sounding more like "mrmrmrmrmr". I think it is so funny and cute the way he does it, I laugh every time. I've been trying to get a good little video of him doing it all week but this is the best one I could get without him getting distracted by the camera and trying to grab it.