Spontaneous body contractions of Hydra (65x acceleration). The spontaneous contractions are shrinkages of the body column that occur periodically in the absence of any exogenous stimuli.
Reference: Murillo-Rincon, A.P., Klimovich, A., Pemöller, E. et al. Spontaneous body contractions are modulated by the microbiome of Hydra. Sci Rep 7, 15937 (2017) doi:10.1038/s41598-017-16191-x