The guy lost his snake so he put up a lost pet poster. The lady sees the poster and the viewer can imagine she is concerned - a 30 ft snake is dangerous. If the snake is loose for long there will be a lot more "lost pets" in the neighborhood.
I had no idea, so i asked my AI overlord to explain the joke to me.
"Ah, that sounds like a classic Gary Larson twist! Without seeing the specific comic, I can offer a general interpretation of what the humor might be in a Far Side comic featuring a lost 30-foot long brown snake named Ginger.
The humor here likely lies in the absurdity and contrast of the situation. On one hand, you have a potentially menacing, large snake, which people would typically find intimidating or even frightening. On the other hand, it's being treated as if it's a harmless, lost pet with a cute, non-threatening name like "Ginger." This juxtaposition of a dangerous creature being treated in a domestic, almost tender manner is a common type of humor found in Far Side comics. It plays on our expectations — you'd expect a lost pet poster for a small dog or cat, not a huge snake!
The comic might also be playing with the irony of how a 30-foot long snake could possibly be "lost" given its size, making it a humorous commentary on how we sometimes overlook the obvious.
Far Side comics often have these layers of humor, where the situation is exaggerated or presented in a way that's contrary to what we'd expect in reality".
Just to add another layer to this. I uploaded the image to the AI and asked what was funny. It insists the snake is wrapped around the telephone pole, the fence or the man's waste.
The idea of someone having a pet snake in 1982 would have been so bizarre that it would be deemed comical. That said snake is called "Ginger," a typical name for a harmless cat, not a 30-foot python reinforces that. This would probably have raised a sensable chuckle back in the day, but I don't think it really stands up to the test of time.
Could it be poking fun of Thomas Jefferson as he was a red head and the snake's name is Ginger? The comic is from 1982. How long has Ginger been a term for red heads?
I remember reading these in the 90s and thinking they were funny. It's amazing how humor changes over time. It helps put other cultures humor into context considering these were written at a time when my culture was very different.