P+S, to appear in the wake. The wake modes for a freely vibrating square cylinder at low Re, therefore, must be a symmetric one such as 2S or C(2S), 2P and 2P+2S. Since, FFTs confirm an absence of 1:2 type even sub-harmonic synchronization, we can rule out the possibility of 2P mode to appear. Since, the periodic synchronization is 1:1 or 1:3, we expect respective 2S, C(2S) or 2P+2S mode to be present depending on the resonance branch. For the quasi-periodic galloping, where the sub-harmonic synchronization is not purely 1:3, the wake mode is 3(2S) or unstable 2S.