Why do dead lobsters smell like ammonia?

The smell of ammonia from dead lobsters is due to the breakdown of compounds called trimethylamine oxide (TMAO) and dimethylamine oxide (DMAO) in the lobster's body.

When a lobster dies, the enzymes that normally keep these compounds in check are no longer active, and the bacteria in the lobster's gut begin to break down the TMAO and DMAO into ammonia and other foul-smelling compounds.

The concentration of ammonia in dead lobsters can be quite high, and it is this ammonia that is responsible for the characteristic smell.