Meet Sarah, an American who moved to Manchester.
After a long day at work, her British colleague Mark said: "I'm absolutely knackered."
Sarah, thinking he was talking about farm animals, replied: "Don't worry, you'll recover soon!"
Mark just stared at her: "Knackered means tired, Sarah. Tired."
Lesson learned: "Knackered" = Exhausted. Not a veterinary term. π