According to my mum: “if you even miss a single day they throw the entire jury out and have to restart the whole court case again so that the new jurors can hear all the evidence”. I feel that would make longer cases exponentially impractical.
I can’t find anything about this on the internet, other than for someone asking this question in America.
They might call in an alternate juror who went through jury selection and has heard the same evidence, but doesn’t participate in deliberations unless they replace an original juror.
[ Disclaimer: I’m an American Idiot although I assume reserve jurors are common practice for courts ]
Can confirm for the US at least, I was a backup juror a couple years ago in a rather dull civil case. It’s standard practice here to select 14 jurors so you have 12 plus two alternates. I sat and heard the whole case, then had lunch with the judge during deliberations where we chatted about how stupid the case was.
I suspect they might see it as their duty to point out legal stupidity; if only just so that the jurors are not given a bad impression of the whole legal system.