In the first scene, Paul Baumer (Richard Thomas) is chastised by his teacher (Donald Pleasence) for lack of attention in class, (specifically for furtively making a sketch of a small bird). He is ridiculed as an 'idealist' and a 'dreamer'.
In the final trench scene, Paul sympathetically chivvies his exhausted soldiers into staying alert for their own safety. Yet moments later he himself becomes (fatally) distracted by a small bird, the same symbol of beauty that had so irritated his mentor three years previously. Other ironic subtleties reveal themselves here. Paul now seeks solace in smoking, a habit he had until now totally despised. (Recall how he had haughtily rejected his teacher's proffering of a cigarette!). Most tellingly, the movie links the image of Paul's drawings as the metaphor for the idealism of the new generation, a hope that died with Paul in the mud of those hellish trenches.
If you enjoyed this excerpt, I recommend the complete film now superbly re-issued (with cuts restored) on blu-ray dvd.