The Cheshire Beagle is a "trick" that Snoopy shows off in strips from April 1967, January 1977, and again in June 1982, January and February 1992, and July 1993.
The first time Snoopy does the Cheshire Beagle trick
Based on the Cheshire Cat character from Alice's Adventures in Wonderland, Snoopy grins widely, causing the rest of his body to disappear.
1967
In a series of strips starting on April 18, 1967, the Cheshire Beagle makes his first appearance when Linus van Pelt
Linus and the Cheshire Beagle in 1967
is shown reading about the Cheshire Cat in Lewis Carroll's Alice's Adventures in Wonderland. Sitting next to Linus, Snoopy grins, causing his body to disappear and leaving only disembodied grinning teeth.
Linus is initially startled. He tries to discuss it with Patty, who states that such a thing is impossible. He then also discusses it with his sister, Lucy, who subsequently threatens Snoopy with violence if he tries the trick on her.
Snoopy mentions that he has been able to perform this trick for years, and refers to it as a "conditioned reflex."
1977
The Cheshire Beagle re-appears in three straight Sunday strips from January 1977.
In the strip from January 9, 1977, Snoopy is shown
Lucy and the Cheshire Beagle in 1977
telling the story of Alice in Wonderland to Woodstock. When he gets to the part of the story involving the Cheshire Cat, Snoopy decides to demonstrate his Cheshire Beagle trick to Woodstock.
When asked by Woodstock to demonstrate the trick again in the strip from January 16, 1977, Snoopy complies but is unable to return. Told by Snoopy to get help, Woodstock returns with the fire department, who spray Snoopy with water.
In the strip from January 23, 1977, an embarassed Snoopy has still not returned. Charlie Brown, describing it as a "re-entry problem," seeks help from Lucy, who solves the problem by slapping Snoopy, who instantly returns to his visible form.
1982
In a strip from June 20, 1982 (Father's Day of that year), Snoopy repeats the Cheshire Beagle trick and says that it was taught to him by his father.
1992
The Cheshire Beagle makes further appearances in the strips first published on January 8 and 29, and February 3, 1992. While Charlie Brown is reading Alice's Adventures in Wonderland aloud, Snoopy again performs his Cheshire Beagle trick. He varies the trick by disappearing completely apart from his nose and vanishing completely apart from his ears.
1993
The Cheshire Beagle makes his final appearance on July 11, 1993 when Sally reads Alice's Adventures in Wonderland to Snoopy. The beagle makes his body slowly disappear upon grinning. He then shows just his nose and mouth, and eventually his eyes appear. Snoopy's eyes, nose and mouth move around on his face as it starts to reappear. He feels dizzy and orders Sally to read something else quickly.