Aziraphale's will had finally broke. Not literally, of course. No, he'd simply decided to give Crowley's plants a break. He'd water them, so the demon didn't have to threaten them, or pluck their innocent leaves. He let himself into Crowley's apartment, impressed at the size and decor. Crowley was always just there, on the cutting edge of modern style. But, Zira was an angel on a mission, and so he went to the kitchen to find a watering can, a pitcher, something he could use to water the plants.
He ended up using an oversized glass, and he ended up dropping it when he realised he wasn't alone, and the presence of another startled him.