Part of daily operations for the Danish State Railways: coupling and decoupling at stations during passenger service.
In this video we see an EMU IR4 (Litra ER 2101) arriving at Copenhagen Central Station and decoupling on the go from the attached DMU IC3 (MF 5279)
Among other things, the interesting fact of these trainsets is that the flat rubber-contoured face actually opens when the trainsets are coupled so that passengers can easily move from one unit to the other. The train driver seat and control panel are attached to the front and collapse together to make room for the front to open.
The decopling operation is announced by the train driver to the train conductor sitting in the driver's cab in the back unit. The train conductor accepts the the decoupling , which releases the hook and splits physically the trainsets. The rubber sealings are then re-inflated during the halt to continue the journey.