Numbers!

This activity I think is perfect for students involved with numbers, such as engineering students.
First, they all have to sit on a line, and teacher's going to state a rule, for example:
pair numbers.
All students must say their numbers in order and only the ones included by the rule should stand up.
When somebody makes a mistake, that rule must go on until the mistake is solved and the number of students is over.
As the activity gets warmer, teacher should state more complicated rules, for example:
prime numbers.
When all students have said their number (in which case, it's because nobody made a mistake) the numbers should go on until somebody makes a mistake and then a new rule is stated.
I hope I didn't make you feel sleepee with this idea.