Grey Matter took a while to notice the knock, however, as he was deep in his own mind, as he saw it, fighting off the demons. As the door knocked three times, he processed it in his mind.
He was snapped back into reality.
He noticed a sound coming from outside of the Kitchen.
He realized the sound was somepony knocking on the door.
And so, Grey Matter labored to get up and lumbered to the door, still not fully aware, so all he heard throught the door was "Mphey Maffeh? You Hmph? Ish meff Herth Mmphitor. I Fusth wanfed to shepf on you." Eventually, Grey Matter uttured, "Heart Monitor? Yeah, I'm home, but I couldn't catch the rest of that, come again?" Which he said barely audibly for Heart Monitor, finally opening the door so all he could hear was "Come again?"