Okay, I’ve heard of “throwing things against the wall and seeing what sticks” in the metaphorical sense, and in the literal sense of throwing spaghetti at the wall to check whether it’s done (though I’ve never heard of anybody actually doing that).
But this baffles me. As well as Ma’s friend’s spit-take.
Comics I Don't Understand 
I’m with you, it is simply thrown together and stuck to the wall. I was scratching my head as well. Grimmy must have some sharp toenails. The spit take is because he is stuck to the wall where she didn’t expect him, I guess.
The is a “yes, that’s it” cartoon. The phrase “see if it sticks” is taken literally. Nothing more.
Is the neighbor / friend doing a full spit-take?
Without the image of the dog on the wall (how does the bowl and its paws stick, anyway), i would have thought this was a culinary experiment to see what “sticks” in the stomach. If it doesn’t stick, out it comes.
I have actually thrown spaghetti at the wall to see if it is done. This was as a student and more because “I’ve heard you throw spaghetti at the wall to see if it is done; let’s try it” rather than a regular part of the meal preparation process.
It is important to note you only throw one strand of the spaghetti at the wall, not the whole bowl covered in your sauce of choice, as Mrs Edna Bloggins*, our landlady, pointed out when surveying the scene.
*Mrs Bloggins is an invention for comic effect. Our landlord was in fact faceless Manchester City Council, who had decided to move normal people and families out of their newish (less maybe 5-yo) pref-fab concrete blocks of high-rise deck access council flats in Moss Side and let the empties out to students until such time as they could demolish the buildings and replace them with low-rise council houses instead. Our rent was £11.97 a week for a flat, divided between three students – this included hot water and heating. Even in 1977 that was cheap – basically $360 each for the entire year . And only ten minutes walk from the university.
Sometimes, when the cartoonist is out of jokes, he’ll just throw something together and see if it sticks.
When I first saw this cartoon, my eye was drawn to Grimm and I thought it was one of those one-panel cartoons that you’re supposed to orient vertically.
But then I saw the two ladies at the table, and I was a bit disoriented for a few seconds as I tried to figure out what was going on.
The friend’s spit-take mirrored my disorientation.
If I were enjoying a nice cup of tea and suddenly got a whiff of ad-hoc dog food, I think I’d feel like throwing up, too.
P.S. I once heard a story about someone using the “spaghetti” method to determine when it was time to put underwear in the laundry.
Once anything sticks, the wall goes Escher on you.
I think Mr. Peters was having trouble coming up with a good idea for the strip, so he decided to throw this idea at his syndicate to see if it would stick…