Recently I've read Zen And The Art Of Radiotelegraphy by Carlo Consoli, IK0YGJ. I must say, it's a great book, and as a new CW operator I've found plenty of useful information in it.
What especially catched my attention was:
This freedom of manipulating a telegraph key produces very interesting phenomena: the laughter, HI, for example, is not transmitted accurately H (four dots), followed with the proper spacing by the I (two dots), it but is transmitted as four-dots, a light syncope, a dot, another syncope and a final dot. The resulting sound is incredibly similar to that of a real laugh. Once heard, it cannot be forgot.
Sadly I couldn't find a recording of a proper HIHI sound, nor I encountered it on the air. Maybe someone knows a video on YouTube that demonstrates how HIHI supposed to sound? Or, if it's not too much trouble, could you please record this sound?