Fingernails have nothing to do with the slaps because you don't use them when you slap. There are other techniques that involve the use of fingernails, but your standard slap, cupped or open, is not one of them.

Open slaps can be achieved in a number of ways. On Djembe, for example, you do not cup or bend the fingers in order to generate a Slap tone. Instead, you tilt the hand slightly, which forces the fingers to make contact at an angle. Getting good slaps on the Djembe was tough for me at first because I had been playing Congas for so long, curving my fingers ever so slightly ... even when playing Open Slaps.

It's the "whipping" action and velocity that gets the good slaps.

Maybe Giovanni plays some acoustic or classical Guitar as well. Or perhaps it's a cultural thing. I'm a gringo, so I don't know the answer to the culture possibility. I let my fingernails grow a bit long at times, which is good for some hand drum techniques and bad for others.

Yes, exactly. I use my fingernails for various sounds and techniques on the Congas and other hand percussion instruments ... but playing slaps is not one of those techniques.

treefrog88 thought that the fingernails may help with the slaps and the "crisp" sound Giovanni gets on the Congas. This is not the case and the fingernails have nothing to do with slaps or the "crispness" of the sound.