Critics note Matthew 5:13 -- "You are the salt of the earth. But if the salt loses its saltiness, how can it be made salty again?" and point out that salt (sodium chloride) does not chemically lose its flavor, claiming Jesus made an error.

However, a closer look at the Greek and the cultural context resolves this. The word here is moraino, meaning "to become insipid". In the context of this verse, it refers to Christians being the "salt" of the world. Christians themselves won't lose their "saltiness" except in one way - by becoming like the world. Hence, if one wants to know how salt "loses" its savor, the answer is by contamination.

Furthermore, Dead Sea salt in the ancient world, unlike modern refined table salt, did lose its flavor. Ancient "salt" wasn't pure sodium chloride, but NaCl mixed with other rock and mineral matter; if it was allowed to get moist, the NaCl would dissolve out and leave behind a pile of tasteless dirt. Thus, in order for the salt to preserve its savor, 'the world' had to be kept out of it.

It is also noteworthy that in context, this isn't salt used for consumption in the first place. Malina and Rohrbaugh note that the "earth" here alludes to an earthen oven outside the house which was used to bake, and had a dung heap nearby; the dung was used as fuel and was salted to use as a catalyst to make the dung burn. The reference is to salt that is so exhausted that it no longer makes the dung burn -- not to how tasty the salt is.