What important ingredient should customers be aware of in the key lime pie?

The ingredient that customers should be particularly aware of in key lime pie is the inclusion of eggs. This is significant because eggs serve a crucial role in the preparation of the pie, often used to thicken and stabilize the filling, giving it that classic creamy texture that characterizes key lime pie. Customers with allergies or dietary restrictions related to eggs would need to be informed of this ingredient to avoid adverse reactions.

In the context of the other options, while key lime pie does contain dairy (from the condensed milk), fruits (specifically key limes), and some variations may involve nuts (like a nut crust), these are not as critical in terms of allergy awareness compared to eggs, especially since egg allergies are quite common. Therefore, highlighting the presence of eggs is paramount for ensuring customer safety and dietary compliance.