For an atom on the surface of a conducting material, the Kondo effect describes the interaction between the spin of the ‘impurity’ atom and the conduction electrons in the surface, and is manifest as a minimum of resistance at the so-called Kondo temperature. Experimental signatures in the complex many-body systems of magnetically doped materials can be difficult to disentangle and interpret, but in the case of cobalt atoms on a noble-metal (111) surface, there had been consensus: the zero-bias anomaly (or dip) in the differential conductance seen using scanning tunnelling spectroscopy (STS) is linked to the Kondo effect.