The abundant production of top quark events at the LHC allows testing the standard model in unprecedented ways. The relative probability for W bosons to decay to a muon or a tau-lepton is measured, selecting events in which a top quark pair decays to two opposite-sign leptons plus jets through W bosons. The measurement confirms the universality of tau and muon couplings to the W boson with the highest precision, to date. In a second analysis, charged leptons are again used to select di- and multi-lepton final states with high jet multiplicity. The kinematic, multiplicity and flavour properties are input to a multivariate discriminant to recognise and establish evidence for the extremely rare production of four top quarks in an event.