two men...

2 men walking towards each other on the same side of the road, both dragging their right legs behind them.
As they pass each other, one looks at the other and says referring to his leg "Vietnam 30 years back".
The other then says referring to his leg
As they pass each other, one looks at the other and says referring to his leg "Vietnam 30 years back".
The other then says referring to his leg
Spoiler: