There can also be problems when the instructor has a significant foreign accent....
During an early ciné weave sortie ("Co..........mmence. Track, track, throttle back, roll, airbrake, power") with our French exchange officer, I was at the 'power, stage when he announced "Poweurre eurff", which surprised me. So I did as he instructed and closed the throttle, whereupon the lead Hunter disappeared upwards and we knocked it off....
"Non, non - I say poweurre eurrpp, not poweurre eurff!" he explained...
Great chap, but the crew room would go IMC with garlic when he opened the lunch box his wife had provided! Normally on asked one's instructor whether he would like a coffee during the debrief; Roger would always reply "Non, merci. But eef you 'ave a little red wine...??". So one day towards the end of the course, that's what I offered him after an ACM trip. It was accepted with alacrity!
Another TWU instructor was a Luftwaffe exchange pilot. One day he went off with his student for an ACM 1v1 trip. "Outwards turn for combat...go" "Inwards turn...go!" was quickly followed by his student calling "Splash, knock it off" as he sat firmly in the Luftwaffe mate's six. So they set up for another run....with the same result. After which his student called "Just like the war, eh Reiner?"....
The reason for his success was that the said student was in fact a highly capable Gnat QFI on his way to flying the Jaguar!