A perfect example is the John Bodkin Adam's case. Not jurors, but leading prosecution witnesses who were nurses. One evening after giving evidence all 3 nurses sat on a train together and discussed the case. That discussion from the train went straight back to the defence team. Needless to say Sir Frederick Lawrence has a field day with it in court and won the day.
To this day Adam's could have been this Country's worst ever serial killer, but he was acquitted.