The cup was out, settled in the center of the table. While he wasn't doubting himself, his idea, he was still reluctant to let the cup out of his sight.
But if he was going to entrust it to anyone, Bellatrix had the most to lose with her failure. She was easily his most devoted, and he had little doubt she would carry out his instructions to the letter.
He'd borrowed a house elf from another of his Death Eaters, and he could hear the creature moving about in his kitchen. When the knock came, he ordered the elf to ready two glasses of wine - he himself rose to answer the door.
After ascertaining it was Bellatrix, he released the wards to open the door. "My pet. Good evening," he said to her as he stepped back and gestured for her to come in. "Have a seat," he murmured.