Can a witness change their facial expression in the course of giving evidence?

Changes in a witness’s demeanour can be highly instructive; in Police v. Razamjoo, [2005] D.C.R. 408, a New Zealand judge asked to decide whether witnesses could testify wearing burkas commented: . . . there are types of situations . . . in which the demeanour of a witness undergoes a quite dramatic change in the course of his evidence. The look which says “I hoped not to be asked that question”, sometimes even a look of downright hatred at counsel by a witness who obviously senses he is getting trapped, can be expressive. So too can abrupt changes in mode of speaking, facial expression or body language. The witness who moves from expressing himself calmly to an excited gabble; the witness who from speaking clearly with good eye contact becomes hesitant and starts looking at his feet; the witness who at a particular point becomes flustered and sweaty, all provide examples of circumstances which, despite cultural and language barriers, convey, at least in part by his facial expression, a message touching credibility. [para. 78]