Mitch4 sends this in: “OY because it’s a pun, CIDU because the specifics are obscure. “Impeccable” works as an OY because someone wearing a suit of armor can’t be pecked. But who is “Gertrude the Brahman” and does she wear armor and why the expression “knight suit”?”
Comics I Don't Understand 
Had to google it. It turns out that Brahma is a variety of chicken. So Gertrude is just a hen. As far as I can tell, “Brahman” instead of “Brahma” is incorrect.
Presumably she’s wearing armour to protect against pecking.
https://en.wikipedia.org/wiki/Brahma_chicken
Those things really freak me out, too. I’ve watched a few YouTube videos of giant brahma chickens walking around, and between their size and their feathery legs, something about them just makes my skin crawl.
Brahman is [also] a kind of cattle. Or an important concept in Hinduism.
But probably the “chicken” sense best connects with mention of “henhouse” and the im-PECK-able pun. If we overlook the spelling issue.
I think it’s a typo… and a very geezer-alert: The Boston Brahmins are members of Boston’s historic upper class: https://en.wikipedia.org/wiki/Boston_Brahmin
… but then I’m lost on the reference to knight suit… or henhouse….? Idunno.
Impeccable — of course you have heard this old joke:
“Bad news from the doctor: my wife is unable to conceive. She will never be able to bear children. She is unbearable.”
“No, that’s not the right word. The word you want is inconceivable.”
“You’re both wrong. The word for her is impregnable.”
We discussed this in the comments for that that strip. It goes to the notion of “pecking order” in a henhouse. Becoming “unpeckable” might seem to make one the top chicken. although from what I recall it’s not that simple in chicken societal dynamics.