How do you tell a bad egg from good without opening it?

Unfortunately, you can't tell a bad egg from a good one without opening it. There are some tricks and tests, but none are foolproof:

Methods that might work (but aren't reliable):

* The float test: Place the egg in a bowl of cold water. A fresh egg will sink to the bottom and lay flat. An older egg will stand up on its end, and a bad egg will float. This is because as an egg ages, the air pocket inside gets bigger, making the egg less dense. However, this doesn't necessarily mean a floating egg is bad – it just means it's old.

* The light test: Hold the egg up to a strong light source. A fresh egg will be opaque with a clear yolk. A bad egg will have a dark or cloudy yolk and a visible air pocket. This method isn't always accurate either, as some eggs might have dark yolks due to the breed of the chicken.

Reliable methods:

* Smell test: Crack the egg and sniff it. A bad egg will have a strong, sulfurous odor.

* Appearance test: A bad egg will have a green or black ring around the yolk, or the white may be runny and watery.

The best advice: It's always best to check the "sell by" date on the carton and use your best judgment when choosing eggs. If you're unsure, it's always better to err on the side of caution and throw it out.