spanish joke

[pogo]

hi guys

i received this Spanish joke in my email yesterday and it confused the hell out of me, fortunately today i got a translation but i was wondering if someone could explain some of the syntax that is used. The joke is:

¿Cuál es el colmo de un gallo?

Pedir lapiz teniendo plumas

which apparently translates as

What's the height of stupidity for a rooster?
To ask for a pencil with so many pens at hand.


The joke being that plumas means pens and feathers so it's not a joke that translates well


First off what is the meaning of colmo ? On this site it says 'last straw' on the email it says 'height of stupidity' so that's a bit confusing.

Secondly when do you use cuál and when do you use qué ?, i thought cuál meant which so this also threw me.

Next is the use of pedir at the start of the punch line, is it common to use a verb in its infinitive form like this because this is the first time i've seen it.

thanks for any help clearing this up.