He picked himself up and we noticed a harmless looking damp patch on his bottom. But as the first act continued, the left sleeve of his white shirt gradually turned redder and redder, and he seemed not to be noticing.
The blood transferred to his right hand, and onto other actors, and you could feel people in the audience praying that he hadn't severed an artery.
Michael Matus as the Italian opera star passed out on the double bed, but I think that bit was in the script. As the action continued on one side of the stage, a bellboy appeared on the other with a dustpan and brush and swept up the jagged shards. He had to beat a hasty retreat as the lights came up for the next scene, but he returned a few minutes later, in the half light, to complete the job.
This was one of the most deftly excecuted piece of improvised stage management I've ever seen. Well done, that man. The act finished with a great roar of approval - the audience was enjoying the show anyway, but this was a "live theatre" bonus - and the buzz was tangible.
It also fitted perfectly with the show's momentum, which is one of "the show must go on," as Max steps heroically into the breach as Otello, and was now doing so in even more heroic circumstances.
Girls were giggling, guys were gawping, one or two punters thought it might even have been a deliberate part of the show. The company manager was no doubt back stage dealing with the crisis, but no house manager appeared to pacify the public. Instead, we converged on an usher with an ear-piece who revealed that the performance would continue after an extended interval to get Damian treated and bandaged.
A disembodied voice at the start of the second act thanked us for our patience, but failed to supply any medical report. After the second big number, the title song duet between Humbley's Max and his fiancee played by Cassidy Janson, she asked him if he had something up his sleeve.
It didn't sound like an improvised line, as the plot is thickening and surprises accumulating, but Humbley kept a straight face (we didn't) as he replied, "What's up my sleeve, my dear, you won't believe!" The tenor had obviously been lent a tourniquet by this stage.
Then, another mini-catastrophe: Janson's dress came apart in his hands as a shoulder strap slipped its mooring. They just about struggled through a few lines of dialogue before he could bundle her towards the exit. With all the door-slamming to follow, I fully expected door knobs to come away in people's hands, or Paul Farnsworth's flimsy mauve sets to start collapsing inwards to the floor.
But none of that happened, and the cast, led magnificently by Humbley in tandem with Matthew Kelly, skipped through to a delirious conclusion and a rapturous, sustained reception, every single minute of it richly deserved.
En route, Kelly's banana boat codpiece seemed to have come oddly adrift from the rest of his Othello costume, but I think that was meant to be part of the fun. Or at least I hope it was. At least Sophie-Louise Dann didn't burst out of her gown when hitting a top note in her show-stopping operatic routine. If she does one night, Michael Matus as the Italian "Il stupendo" is ready with the riposte that he uses anyway: "Che meloni!"
A special cheer, then, for Humbley who's terrific in the role. And it was interesting that no one held back from the considerable man-handling and shoving about he gets for the rest of the play. I just hope his wound is not serious.
Either way, I'm told he is fully entitled to sue the management. In which case, the producers might well soon be passing the hat round, judging by the paltriness of Saturday night's small but perfectly formed audience: then it really would be a case of Lend Me Tenner, or multiples thereof.