I had the opportunity to eat some betel leafs today. My first impression was that it was like chewing on a spicy local anesthetic with a hint of black licorice. Which turns out to be pretty close to the truth. Betel is related to the plant that is the source of black pepper (hence the spiciness?), its oil contains eugenol (which is the major component of clove oil, is used as a local oral anesthetic, and is the source of the typical smell of dentists offices), and its oil contains anethole, one of the components of licorice root extract.
The initial chewing not being wholly unpleasant, I decided to make tea out of the betel leaf. The tea was much less strong than the leaf itself. I think from dilution and because the oil in betel leafs is held in glands in the middle of the leaf and the leaf is pretty tough and waxy, so the oil probably doesn't extract very well. The tea wasn't spicy at all, and had a much less powerful anesthetic effect. Drinking the tea gave an overall sensory experience similar to what I imagine one would experience if eating licorice in a dental office.
In 1999, there was actually a study published about how people associate the smell of eugenol with either positive or negative emotions depending on their attitude towards dental offices. Personally, I'm pretty indifferent towards dental offices, although I generally don't associate them with food, which is probably why I thought the betel leaf taste was pretty odd for a food. Also, I tend to prefer that my food not make my tongue go numb. However, given the huge popularity of betel leaf consumption in certain parts of Asia, I guess this is a cultural phenomenon. I wonder if people who spend more time chewing betel leafs than sitting in dental offices associate dental offices with betel leafs, and start getting cravings when they're having their teeth looked at.