Cold joke

We discussed about joke in class on last Saturday. I though it was very interesting. First, we listened to a lot of jokes on the CD player. Then each group had to prepare 2 jokes and told to everyone. Some of jokes were not funny at all, but other jokes were funny. Our one of joke had been considered the funniest joke by classmate. The joke was from internet and contact was:
A: Do you know what the pencial’s family name is?
B: It is 蕭. (because 削铅筆)
I think it is really a “Cold Joke”.