Demonstrations need to be appropriate to the ability level of the student.
The higher up the syllabus, the more realistic the material needs to be.
Always use caution and put the wellbeing of the student first.
Be careful with inexperienced students.
Awkward people who 'try it on' - consciously or not - can lead to injury on your
part.
Treat all demonstrations as being potentially dangerous. Keep your mind and your
eyes on the attacker.
Do not trust new people. Do not make any assumptions regarding their conduct.
What is the purpose of the demonstration?
Is it something the student can understand and reproduce?