Which of the following is NOT a characteristic of an express contract?

An express contract is characterized by the clear communication of terms and agreements between the involved parties. These contracts can be formed either through oral or written means, which means they do not have to be solely in a written format. Therefore, saying that it "must be written down" is not accurate; an express contract can exist as long as there is mutual agreement, which encompasses both verbal agreements and written ones.

The elements of mutual agreement and clear communication are both fundamental aspects of express contracts. Thus, the assertion that an express contract must be recorded in writing is precisely what makes this option the correct choice, as it falsely narrows the definition of an express contract.