How to write untestable code

In the talk “Unit Testing” within the series of Google “Clean Code Talks” Miško Hevery first asks the audience how they would write untestable code. There were not much answers although we are all very good at it. Question: “How to write untestable code?” Answer: “I don’t know. It just works.” Fortunately he also offers ideas how to write testable code during the talk.