The ever present crab has its eyes hidden in blackness, not unlike Marvin Martian.
The shark's roar was actually a lion's roar. Not to mention, it's Tanner's roar. Tanner the lion was known for being in the MGM logo from 1934 until his death in 1956.
The First Appearance of Spike
Spike slyly breaks the fourth wall with a couple of sidelong glances.