The contraction behavior in Hydra

Example of Hydra spontaneous body contractions (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