The Matterhorn Affair - S3-E24
Continuity mistake: Marvin has a homing-pigeon hat. When he's pushed off the precipice, his hat falls off. After a shot of his sister screaming, we cut back to Marvin still falling, and his hat is back on, falling off again. But it's somehow back on his head yet again when he's rescued a few scenes later. (00:38:45 - 00:40:10)