Kuyler is shown multiple times pouring his absinthe and drinking it straight. The traditional French preparation involves placing a sugar cube on top of a specially designed slotted spoon, and placing the spoon on a glass filled with a measure of absinthe. Iced water is poured or dripped over the sugar cube to mix the water into the absinthe. The final preparation contains 1 part absinthe and 3-5 parts water.
At the end of the episode when Inspector LeBrun is interviewing Duncan, Tessa pours a glass of Champagne and it 'fizzes'. When we can see the glass there are no bubbles or other evidence of what is making the fizzy noise.