Appendix. Derivation of the logarithmic spring equation We consider the regime We1 and build a quasi-static model similar to that developed for drop impact on a rigid substrate (Mol´ aˇcek & Bush 2012). The actual instantaneous shapes of the drop and the bath are approximated by relatively simple shapes characterized by a small number of variables. The family of shapes we choose is one consisting of sessile shapes of liquid drops resting on a liquid bath (now not necessarily made of the same liquid as the drop). The reason for this choice is that, in the We1 regime, when the overall rebound dynamics is slow relative to the dynamics of the typical surface waves created, one expects the surface shapes to equilibrate to some quasi-static form (Bach, Koch & Gopinath 2004). If the drop has surface tension σD and density ρD, and the bath σB and ρB, the sessile shape family has dimensionality three by Buckingham’s theorem; it can be parametrized by two Bond numbers A=BoD =ρDgR2 0/σD and C=BoB =ρBgR2 0/σB and by the parameter B=σDBoD/σB. Although in our system we have σ =σB and ρ =ρB, initially we keep these variables separate in order to describe the deformation of the drop and bath independently.