Most people have noticed it . . . WILL FERRELL looks EXACTLY like the drummer for the RED HOT CHILI PEPPERS, Chad Smith.  So Jimmy Fallon had them do a drum-off on "The Tonight Show" . . . and it went in unexpected directions.


First off, Will Ferrell didn't seem completely incompetent.  He pulled off a couple small solos.  Except he was just AIR-drumming . . . it was actually Questlove from the Roots


Then at the end, he busted out a COWBELL . . . and the rest of the Red Hot Chili Peppers came out to do "Don't Fear the Reaper", as a reference to the SNL skit.