1 Prof. Jones: Hey, Junior, I'm having lunch. Want to share?
2 Monty: What do you have today?
3 Prof. Jones: Greek lamb kebabs, with pita bread and a dip made of cucumber, garlic, yoghurt, and lemon juice. It's very nice.
4 Monty: t
4 Prof. Jones: Yes. Tzatz-icky!

Interestingly, Wikipedia defines tzatziki as a "sauce" which is "served with grilled meats or as a dip". Well, I think that's interesting anyway, since I never would have described tzatziki as a "sauce" myself. I would always call it a "dip" - as is evident from Professor Jones's usage in this comic.

Further interestingly, Wikipedia implies that a dip is a type of sauce:

A dip or dipping sauce is a common condiment for many types of food. Dips are used to add flavor or texture to a food, such as pita bread, dumplings, crackers, cut-up raw vegetables, fruits, seafood, cubed pieces of meat and cheese, potato chips, tortilla chips, and falafel. Unlike other sauces, instead of applying the sauce to the food, the food is typically put, dipped, or added into the dipping sauce (hence the name).

If you'd asked me to define what a dip is, the word "sauce" would never even have come into my mind.