Not just applause - that is standard. But multi-party approbation. Leaders and their colleagues all applauding each other, commending the comments of their rivals.
It was a display of solidarity, of unity, of determination to defy terror in the face of the tragic scenes from Westminster. A small thing, perhaps, the collective hubbub of colliding palms. But, in its way, significant.
It is an animal instinct, a social imperative, to huddle together when under attack. But this was also about a declaration of shared values; of democracy and freedom of expression.
Each of the leaders performed their role well, deftly choreographing their condemnation and commonality of purpose.
The first minister talked of the "heinous attack" witnessed at Westminster. Like other leaders, she praised the police, the security officers and others who had tendered assistance. Those who ran towards chaos, to help, rather than understandably fleeing the scene.
Terrorists, she said, seek to undermine, to divide. "They will not succeed", she declared. It was a conscious echo of statements made by others, including the prime minister. It was a deliberate act of consolidation.
Ruth Davidson spoke of a cowardly attack, Kezia Dugdale described Westminster as a beacon of democracy, Patrick Harvie urged a programme of education to ease division.
Willie Rennie told movingly of how he used to walk across Westminster Bridge on his way to work as an MP, no doubt quietly reciting Wordsworth's lines, "a sight so touching in its majesty". Many years earlier, I pursued the same route daily, from Waterloo.
Mr Rennie reflected that the splendour he had once witnessed was now associated with brutality and death. One can but hope that Wordsworth's majesty will return.
All the leaders, all the leaders, emphasised that terror must not be allowed to divide communities in Scotland. In particular, that there must be no backlash against Muslims.
Then it was over - and, in further questions, MSPs returned to discussing hospitals, care of the elderly and the like. There was even room for a little muted humour.
Mundane? Of course. Deliberately so. A conscious return to parliament's duty.
After the temporary silence of yesterday, there was an unaccustomed noise in the Holyrood chamber today.