This is an impressive bar trick to do, but since it involves fire and huffing you should not attempt it if you're a lightweight or new to absinthe.
Paul Nathan demonstrates the Czech Huffing Ritual. Most absinthe enthusiasts shun any serving method involving fire, this one in particular, but it's up to you if you dare to try it.
This is a common method of consuming absinthe in Praque. It's a version of the backdraft.