It's a poo flinging machine. Those little paddles have been turned to the side.
upon the approach of the enemy the No2. is to load the device with stools taken from the elsan. When all paddles are fully charged the No2. is to shout "ready". Upon reciept of the word of command the No.1 will then begin to crank the machine at a furious rate, thus launching the projectiles at the onrushing enemy, who will be so appalled as to fall back in disarray.
A crude form of grenade launcher. No.1 observes the target. No.2 rotates the handle, vigorously. Insufficient vigour may lead to misfires. No.3 faces the device at 45 degrees and tosses a string of grenades at it. The paddle strikes the grenade and lofts it high in the air in a forward direction. The whole device is tilted backwards for elevation.
In emergency, multiple throwers could be employed to increase the rate of fire.
Warnings: Accurate lobbing is necessary to avoid a Blue on Blue. As a training method for No.3, pies may be substituted for grenades, or turds for difficult cases. Under sustained use, it will be necessary to relieve No. 2 regularly as a drop in rotation speed has a proportional effect on range.
As you all know, German dugouts were far better constructed than Allied ones. In addition to showers, bars and other welfare amenities, each bunker boasted a full-sized Olympic table-tennis table. If only one off-duty Hun was available, the Oberkommando of the Reichs Heer provided the automated ping-pong machine illustrated here. Apparently Hindenburg was a keen fan of table tennis and won the Silesian Open championship in '04, '05 and '07...
Judging by the gearing, it's designed to spin fast.
It could be for noise generation but the reach of the arms would suggest that it's purpose was to move air -- so my edumacated guess says its for gas dispersal. Gas would collect in shell holes and trenches so the strange shape of the paddles might be for 'scooping' low lying gas up to the height of the parapet where it would be blown away.