Snape clung to his own focus - diamond-hard, bedrock-steady - needing both desperately, as he was buffeted and whirled and battered by the disorienting barrage of physical minutiae and eyeblink sensory hallucinations (really, if the boy's wand was that big and had that much of a knob on the end, Snape was sure he would have noticed!)
It was all Snape could do to devote his besieged attention to both the outside world - and the increasingly wobbly cup of crushed pearl shell - and the polyphonic cacophony of Al's consciousness.
At last the attempt was over, in the soft susurrus of pearl shell grains, raining down from the tilted cup onto the workbench.
Snape could have left Al's mind at once, but he stayed behind, to offer a moment of silence, solidity, support.
He thought it would be a sensation that Al would appreciate.