M*A*S*H - Concrete Floor
This is the M*A*S*H episode where everyone got tired of the dirt floor in the OR and decided to lay a concrete floor. It's pretty late into the series because Charles is now there. Anyway, it makes no sense because previous episodes from as far back as the second or third one show the OR with a concrete floor. I am an avid fan of M*A*S*H and never have I seen a dirt floor in the OR, except for the episode where they claim to be laying one. THEN they made the floor look like dirt.
In fact, in the episode where Henry Blake gets killed, after Radar announces his death in the OR, someone drops a surgical instrument on the concrete floor and you can hear it very clearly.