When the Professor releases the Pigeon at the end, everyone watches it fly off to their left except Mary-Ann and Ginger, who look straight ahead.
Directly after Gilligan finds the giant spider in the cave, the Skipper and the Professor are developing a photograph. Between the slats on the window, Gilligan's red shirt is visible, revealing that Bob Denver is waiting for his cue to run into the hut.
Even though the castaways had supposedly explored the island extensively, they never encountered the giant spider before this episode.
Six of the seven castaways posed for a picture in front of the Minnow to send to the homing pigeon's keeper, but the Minnow was destroyed in the first season.