Gilligan shoots off the revolver three times when the Skipper rouses him from sleep while he's on sentry duty. However, there's no recoil when the gun goes off, indicating that there's no real bullets in the gun.
After Gilligan stumbles and slides down the muddy slope, just before landing in the water, Denver's leg pushes off the edge of the bank to reveal that the slide is merely a mud-covered strip of fabric or plastic that tenses as he pushes off with his foot.