When Jesus orders the tomb opened, Martha objects that by this time there will be an odor because Lazarus has been dead four days. Her response is practical and painfully realistic.
John again stresses the duration of Lazarus' burial at the very moment the tomb is opened.
Jewish burial practices could include washing, wrapping, spices, and placement in a tomb, but they did not involve Egyptian-style embalming intended to preserve the corpse indefinitely. Decomposition therefore proceeded normally. In the climate of Judea, concern about odor after several days would be entirely natural.
The text does not invite theories that Lazarus was merely unconscious or recovering from illness; Jesus has already told the disciples plainly that Lazarus is dead.
The physical detail gives the sign its uncompromising setting. Martha expects the consequences of death, not a patient waiting to awaken.
Opening the tomb therefore confronts everyone present with what has already become irreversible by ordinary human means before Jesus calls Lazarus out.