With the use of falsetto, men can achieve a sound quite similar to that of castrati. When you get used to the pitch, you realize that the timbre is distinctly male, or at least not female. That's what gives the voice the quality that many people describe as "angelic." Some even prefer the countertenor to the female voices. However, falsetto is difficult to master, and only with a great amount of talent and hard work you can be a good countertenor.
Frufru's favourite countertenor is without doubt Philippe Jaroussky. Here, at the "Artiste lyrique," he sings Vivaldi's Vedro con mio diletto (beating Roberto Alagna in the competition)
Something for coloratura lovers:
Just in case you don't believe their speaking voices are "normal" (or that they don't have a sense of humour) - Sombrero:
Countertenors can be encountered even on the pop scene. Just for fun, here's Vitas's Il dolce suono (Lucia di Lammermoor):