In "Opposite Day," Gary tried to do the opposite of his stereotypes by barking like a dog.
In many episodes, it has been indicated that Gary is very intelligent (for a snail at least). In "The Secret Box," Gary responded to SpongeBob's question with "Meow-no." SpongeBob did not think much of it and replied, "Aww, what do you know? You're a snail!" SpongeBob did not recognize it as special, meaning this is not the first time Gary spoke. In "The SpongeBob SquarePants Movie," The Citizens of Bikini Bottom were chanting, "All hail Plankton," while Gary chanted monotonously, "Meow, Plankton." He may even be more intelligent than all the main characters (excluding Plankton), this is ironic as he is a snail, the biggest hint of which was in "Sleepy Time," where Gary spoke in his dream (that SpongeBob was interrupting) and sounded very old and wise. In the episode "Tutor Sauce", Gary is shown to be a good driver, as he is able to drive through the most dangerous road in Bikini Bottom, with no issue whatsoever.
He had an extensive library, which is a possible metaphor for intelligence. He is a domesticated house pet with similar mannerisms to a cat but also has royal blood as seen in "Rule of Dumb." Curiously, in Rule of Dumb, it proves that Gary and Patrick are cousins, as their fathers were brothers.
It is suggested that SpongeBob had Gary when he lived with his parents as a really young boy. The episode "Treats!" reveals that Gary was adopted. As seen in "Gary Takes a Bath," Gary can levitate and teleport, possibly meaning that psychic powers run in the Star family, as Patrick has psychic abilities. Gary did not appear again after "Help Wanted" until the episodes "Plankton!" and "Naughty Nautical Neighbors." Gary has been to many places including the large Bass Vegas.
Gary had a minor role in the episode "Atlantis SquarePantis." Gary appears wearing a party hat and blowing on a paper horn. Gary is also a very good musician, although he was not part of Squidward's band in the episode "Band Geeks." In "The Paper," he played Squidward's Clarinet very well, and Squidward gets confused. In "Procrastination," Gary played the trumpet. In "Something Smells," Gary played the violin to make SpongeBob cry while chopping onions because SpongeBob told him to.
In "Patty Caper," when SpongeBob blames Gary for supposedly stealing the secret ingredient to the Krabby Patty, Gary describes another suspect—Squidward, and, based on the picture Patrick had drawn of him, Gary must think Squidward is very ugly.
In "Little Yellow Book," he bites Squidward's tentacle because he was saying the horrible words.
The episode "All that Glitters" shows that Gary has a large diamond under his shell. However, episodes afterward do not show the diamond under his shell.
In "Karate Island," when SpongeBob is waxing Gary's shell, he finds his favorite novelty T-shirt that says, "I love Krabby Patties" in a pile of junk inside his shell.
His favorite food is Snail-Po, which SpongeBob once tasted, and later Snail Bites.
In addition, "Your Shoe's Untied" reveals that Gary has feet.
Gary can say the words "Plankton," "Yeah!," and "No."
Also to illustrate Gary's antagonism towards Squidward, in "I Was a Teenage Gary," when SpongeBob answers the door, to Squidward, holding Gary, Gary hisses at him.
Gary has arms as seen in "Have You Seen This Snail?," "The Gift of Gum," and "Grooming Gary."
According to "Gary Takes a Bath," "Rock-a-Bye Bivalve," and "Pet Sitter Pat, Gary can read because in "Rock-a-Bye Bivalve," he is seen reading the newspaper, and in "Gary Takes a Bath," he is seen reading a book called "Snail Jokes". He was also reading a book called "Snail Tails" to Patrick at the end of "Pet Sitter Pat," although due to Gary's lack of English, Patrick could not understand him, as explained when he said "Snail Tails? I thought it was called 'Meow Meow Meow.'"
Gary has many things hidden under his shell: a house, SpongeBob's Krabby Patty T-shirt, a record player, a diamond, and many other pieces of junk.
In "A Pal for Gary," SpongeBob calls him "Garold," meaning that Gary is likely a nickname.
In the pilot episode "Help Wanted", Gary's pupils are small red dots and his meow is much squeakier.
In "Plankton's Pet," SpongeBob reveals he adopted Gary at an animal shelter. "Treats!" supports this, but "Have You Seen This Snail?" contradicts the continuity.
His full name is Gary B. Snail. It's unknown what the "B" may stand for.
He seems smarter than most of the main characters, including SpongeBob, Patrick, Squidward and Mr. Krabs.
In the game Snail Bob 2 you can see a picture of Gary saying "Cousin Gary" implying that Gary and Snail Bob are related.
According to a variety of episodes, Gary may be compared to a cat. His usual way of speech is by saying "meow." In "A Pal for Gary," in the part where the Nudibranch seller shows a portrait of a cat near a Nudibranch and later on shows Puffy Fluffy violently reacting to Gary may be a hint to the fact that Gary has a resemblance to a cat. As first seen in "Dumped," Gary purrs like a cat.
"Meow Plankton" (The SpongeBob SquarePants Movie)
"Meow-No!" ("The Secret Box")
"Meow" (regalish) ("Rule of Dumb")
In "Your Shoe's Untied," "Frozen Face-Off," and The SpongeBob Movie Sponge Out of Water, Gary roars like a lion.
In "The Thing," "What Ever Happened to SpongeBob," and "Grooming Gary," Gary screeches like a cat.