.... or perhaps Catbert's eyes just rejected what he was reading, causing him to go blind. Same as every time someone in this strip has looked at a reference to naughty things, and has cried a similar thing. MAYBE THAT WAS IT.
I think that SA's punchline was the best punchline. Much better than deepakrn's proposal.
This strip is definitely conflating the two. There's no saying I've heard of that speaks of blinding kittens.
A better punchline for the last panel would be Catbert exclaiming, "Argggh, I can't breathe!!!" or something else to that effect. No mashup option, though.