Left hand slap? Well, he's muting with the fingers on his left hand at times and there are some hammer-ons (with his pinky), but nothing really fancy going on. It's basically a matter of getting the muting happening with the left hand. Does that answer your question?
Get the Download helper Firefox addon and donwload the video.
Get VLC media player, and play the video at half speed (The pitch will be compensated and stay the same)
Like 4String said, start slowly and build up your speed as you get more comfortable. You might want to check out the song "Love Games" by Level 42. It's slower than "Traveling..." and the bass line is played using left hand muting (don't expect to be able to play the whole line, just focus on the first few beats of the song after the drums come in). After a while the muting technique will come very naturally.
