Jaques and the lords are back at the forest and, because all of the talking in the play needs to be broken up by something, there's a musical interlude.
Jaques suggests that the guy who killed the deer during the recent hunt should put the deer antlers on his head and be presented to the Duke. (Yep, that's another "cuckold" reference. Check out "Symbolism" if you want to know more.)
The guys sing a song that starts off being about deer hunting but ends up being about how all men are cheated on by their wives.