Question

how does a fused bulb differ from a normal bulb

Answer 1

Obviously  a fused bulb differs from a normal bulb.

A fused bulb has burnt or damaged filament and a normal bulb has a filament which is not burnt or damaged.

Answer 2

In the fused bulb the tongs is broken and in normal bulb it is good and so the fused bulb is not glowing and the normal bulb is glowing 
and fused bulb's circuit is broken and normal bulb's circuit is not broken as shown in figure.