"My sister in law would NEVER approve of you being covered in goo!"
Come to think of it, Justin and Nanase are pretty much ditching school right now. I forget if I explain why they didn't get in trouble for that. Or maybe they did? STAY TUNED!
This is a comic that wound up confusing a lot of people. I would say it's because they're not observant, but I actually think it has more to do with something known as "change blindness" (which I'm sure will never come up again). Simplified somewhat, it's the idea that someone could easily be completely unaware of a seemingly obvious change if they don't actually observe the change happening.
How is that applicable here? Look at Tedd and Grace's shirts in this comic, then look at how they were in the previous comic. Once it's been pointed out, it' should be obvious that they swapped shirts while getting those towels.
Commentary added November 21, 2014