Why is Squealer out at midnight with a paint brush and a ladder?

One midnight, a crash in the barn awakens the animals. They rush there only to discover Squealer with 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).