Star-Crossed - June 15, 1972 - S1-E3
Revealing mistake: Sam stares at himself in the mirror and takes out his wallet to determine who he's leaped into. But the "reflection" in the mirror lowers the wallet and looks back up before Sam does. (00:05:20)
Revealing mistake: When the first fight starts, the Bloober disappears into thin air. (00:04:52)
Shanpû no hangeki! Hissatsu shiatsuken wa mimo kokomo ubau - S1-E16
Revealing mistake: In his close-up when he grins at Ranma after his request to help him figure out what happened to Akane, Ryoga is drawn really obviously with the hair going under his eyebrows. (00:15:00)