It's Sarge's birthday, and Fillmore is helping him celebrate with both a cake and a present he made himself. He found the cactus out in the desert and planted it in one of Sarge's old tires, which he has painted in a horrendous hippie mockery of military camouflage. XD
Note that Fill has cucumber slices on his pizza instead of pepperoni. ^_^
Poor Sarge. I don't know if he'd really like that "camo" tire planter. He looks like he's reminding himself "it's the thought that counts," over and over again.