The first knock, Arthur hadn't been certain that he'd heard. The radio was on and he had knocked a fork off the table. After being under the cruciatus curse, he'd mostly gotten his motorskills back but every so often it came back and it was getting frustrating.
The second knock, however, was clear and Arthur practically jumped up from the table. He grabbed his coffee, hoping he didn't drop that too and managed to get to the door. Opening it with a "Hello" before he recognized who it was that was standing in his doorway.
"Mr. Pucey?" Well that was unexpected. It was no question of knowing who he was. Or what side he was on. Arthur put two and two together, glad that Molly wasn't home and most of his family had been out. "This is an unexpected surprise," he replied keeping his tone pleasant. "I'm afraid that you've caught me in the middle of breakfast. Um... can I help you?"
This was a Dark-alligned individual who could practically do whatever he wanted. Hostility, even though that's what every inch of him was screaming at him to do, would do no good.