What is the meaning of Squealer’s midnight accident, which only Benjamin understands, and why doesn’t Benjamin explain it to the other animals?

Squealer has a broken ladder and a can of paint. Benjamin seems to understand what is happening but declines to share his insight with the others. However, a few days later, Muriel notices that the Fifth Commandment has been changed from “No animal shall drink alcohol” to “No animal shall drink alcohol to excess” (113). Benjamin does not read for the animals until Boxer gets taken away.