The "pump-looking" things are either hydraulic cylinders, or mechanical dampers if the robot is electrically driven. EDIT: I'll accept @50k4's identification as hydraulic springs.
In the "what's going on back here" department, the long thin member is a linkage. It is part of a 4-bar parallelogram linkage which allows the forearm to be driven using a motor which is located far below the elbow (the lowest red piece in your picture). The benefit of this arrangement is that the upper arm link does not have to carry the weight of that motor. Please note that I am using "upper arm" in the anthropomorphic sense. It is the link closest to the shoulder.
The other part of "what's going on back here" is the large blob of metal. Notice that this blob has its top center carved out so that the linkage can nest in there, thus increasing the forearm's range of motion. The blob itself is a counterweight. By adding counterweights, the load on the motors due to gravity is reduced, even though the total inertia that the motor must move is larger.