Example of weak interactions induced by mixing

I understand that weak interactions are the exchange of W and Z bosons between leptons and quarks (as explained in this other question: Weak Interaction), but when I read Light Sterile Neutrinos: A White Paper it stated that:

A sterile neutrino is a neutral lepton with no ordinary weak interaction except those induced by mixing.

What other types of interaction are there if not the mixing of particles? Or is this not the meaning of mixing? Could you give me an example of such a mixing interaction?