Made by: Manyhills
The original strip had the snail saying "You take that back" slowly - however, due to the three-panel limitation, the final panel has to cram "that back", ruining the pacing of the joke (imagine this: "you... take... that back"). This interpretation omits "you", thus improving the joke substantially.
The author's note also includes an alternate take preserving the words and expanding the strip to four panels; it was changed in order to show how Davis could improve within his own limitations.
Obviously if you're telling a joke it's a good idea for the joke to be funny, but even if it is it's not going to work if you don't execute it well, and it's at this hurdle that so many comics seem to fall frustratingly flat. Take this xkcd, for instance - I have no qualms with the underlying joke but the execution is abysmal. Given that xkcd is aimed at a vaguely intelligent audience, it should be taken as read that the reader will know LongtimeUser4's setup is horrifying, and for the comic to explicitly point that out to us smacks of condescension. There really seems to me no reason the comic wouldn't be better if the last two comments were excised completely and it just went straight from first comment to caption.
Now, obviously, Garfield's basic jokes may not be the greatest but in terms of execution it's almost always well done - there are more than a few instances in the SRoMG archive of clangingly obvious errors that require very little effort to fix but make strips a lot better, but the average Garfield strip has very little fat on it (unlike the feline himself), with its setups and punchlines pared to the bone and delivered with ruthless efficiency.
Which makes a strip like this one - the original, I mean - even more infuriating. Jim Davis knows that he only has three panels, why on Earth did he choose a four-word phrase for the snail to say? The original reads like the snail is saying "You take thatback"; it's ridiculous and shoddy and unfunny.
Originally I kept the "You take that back" phrasing and stretched the strip to four panels to accommodate it (shown below). I thought - and still think - that that version is better, but I decided it undermined my point a little, since Jim Davis obviously does not have the luxury of extending the strip to four panels. I wanted to show how the original strip could have been better even within its constraints.
Original strip: 2005-03-14.
Garfield: Snails are slow.