Pun-nishment

Work was visited today by a group of students from Denmark.  I immediately noticed that they weren’t from around here as all of them were blonde and wore Converse All-Stars, they also spoke Danish.  Later that day, I walked by the following:

Coworker #1: The Copenhagen group couldn’t have looked any less interested.
Coworker #2: Maybe it’s cultural.
Coworker #1: Sure seemed like there were a lot of them.  How many three dozen?
Coworker #2: Not quite, I remembered with a simple rule.
Coworker #1: What’s that?
Coworker #2: 30 Danes hath September.