Jim Davis, creator of the lasagna-living Garfield, has finally commented on his infamous May 30, 1990 comic strip in which Garfield's owner, Jon, appears to guzzle a cup a dog semen at a veterinarian's office.

From AV Club:

The "Jon drinks dog semen" theory has been floating around since May 30, 1990, ever since eagle-eyed fans noticed that—at the conclusion of a strip where Jon once again futilely flirts with Garfield's veterinarian, Liz—Jon drinks dog semen. After all, it's telegraphed right there in the punchline, where, after Jon helps himself to an ostensible cup of coffee, Liz drolly responds, "Congratulations, Mr. Arbuckle. You are going to give birth to a fine, healthy litter of puppies."

Ignoring the fact that Liz has some pretty mixed-up ideas about the mechanics of animal husbandry for a licensed veterinarian, the intent here seems fairly obvious. What else could possibly be the joke, if not the idea that hundreds of tiny dog sperm are now worming their way through Jon's digestive tract? Clearly, Liz had just finished jerking a dog off into a coffee cup, and consummate goofball Jon accidentally drank it.