B's

several paradigms with functional, object-oriented thanks to python, smalltalk, clojure
different languages
show paradigms have different "units"
new people :)

C's

lost focus several times
not lowering expectations of the domain

One-liners to do CountdownKata

Python: range(10, -1, -1)
Smalltalk: (10 to: 0 by: -1) asArray
Ruby: (0..10).to_a.reverse
Haskell: [10,9..0]
Clojure: (apply vector (range 10 -1 -1))