My initial reaction, on looking at the work, is to see a war story and brotherhood, simple as that. The plaque reads:

Juan Munoz Spain 1953-2001 Piggy back (right) 1996 bronze Mervyn Horton Bequest Fund 1997 Juan Munoz was one of the few figurative sculptors to uncompromisingly explore the history of the body in art through contemporary philosophical ideas and with a remarkably individual vision. In Piggy back (right), the fiction employed in much of his work is here concentrated on two figures, one carrying the other. They are on their way somewhere, in motion, and from the stance of the carrier they are moving quickly -- silently but quickly. As he leans forward to balance his gait, the carrier feels the full weight of the second figure, as if carrying the trials and tribulations of humanity. The textural qualities of the crumpled clothing, the patination of the skin and dark shadows further fix the idea of an impending moment or event. Munoz's technique of using filled-out clothing to effect the shape of the sculpture provides a trace of the body rather than a strict representation. Equally, the surface is reminiscent of fossilised figures, such as those of Pompeii, which brings a slight chill to the skin. Within the movement their attention is diverted from their task as they glance to their right; whatever they were looking at is now departed, the absence of this distraction adding to the suspense present in the work.

Further reading:

-- A nice interpretation here:

"Is one figure helping the other, like St. Christopher carrying the infant Jesus? Are they two aspects of one person? Or is this an image of the artist shouldering the 'burden' of his art?

Muñoz leaves the interpretation of his work open to the viewer, hoping to draw us into the drama that takes place between the figures, their audience, and their surroundings. These two bald, fine-featured and apparently blind figures seem to be intimately involved with one another, but oblivious to us. Perhaps Muñoz is suggesting that a work of art does not exist simply for the visual appreciation of the viewer, but rather has an internal life of its own in which we are invited to participate...

Piggy-Back also explores the phenomenon of silence and the mystery of communication. We can never know what these figures are saying to one another or to themselves or to us. They are intended, says the artist, to be blind, and are as undifferentiated as possible. As human as they may appear to be at first glance, they are not supposed to be realistic. 'The more realistic sculptures are meant to be,' Muñoz has said, 'the less interior life they have.'"