This chapter illustrates the main warning signals that could help us to detect the flaws of an explanation in physics: internal contradiction (two examples); direct contradiction of a law of physics (one example); indirect contradiction of a law of physics (one example); logical incompleteness of an explanation (three examples); overgeneralization (three examples); incompatibility with a thought experiment (three examples); incompatibility with an unperformed experiment (one example). Finally, we point out that several warning signals can intervene in parallel to question a given text, as shown in a last example (the direction of the current in the batteries). [For the complete volume, "Developing Critical Thinking in Physics: The Apprenticeship of Critique. Contributions from Science Education Research. Volume 7," see ED615688.]