In today’s crop of cartoons, an outrageous Pearls Before Swine and a silly Mother Goose and Grimm, both of them meta-strips and both playing with idioms:
In #1, the characters are treating pieces of wood to psychological pressure, which moves Rat to bash the cartoonist with one of the pieces of wood.
From OED3 (March 2007):
pressure-treated: Of timber: impregnated with a preservative applied under pressure.
[first cite] 1928 Iowa Recorder 12 Sept. 5/2, $5 buys a twelve foot pressure treated hog trough that will last you a ‘lifetime’.
In #2, we have the cartoon character Charlie Brown (visiting from another comic strip) on the couch of a psychiatrist who’s reassuring the boy about good grief. Charlie Brown is famous for using the (American) exclamatory idiom Good grief!
From the Cambridge Dictionary of American Idioms (2003) on good grief:
I am very surprised “I have four computers at home” “Good grief. What do you do with them all?”
Usage notes: often used humorously, when someone pretends that a situation is more serious than it really is: Good grief, look at all this food! Are you feeding an army?