If they are actually just using eye dilation for funny faces, I would be shocked. It's one of those things that's pretty telling physically. Whichever congressman asked that question was NOT dumb.
He asks "Can you say with 100% certainty that TikTok does not use the phone's camera to determine whether the content that elicits a pupil dilation should be amplified by the alogorithm?"
Chew: "The only face data that we collect is when you use the filters to have sunglasses on your face, we need to know where your eyes are."
Congressman: "Why do you need to know where the eyes are if you're not seeing if they're dilated??"
Apparently I can only find primary sources of this hearing on TikTok itself, so: https://www.tiktok.com/@jamiethisyoujeffries/video/721387823...
https://youtu.be/_E-4jtTFsO4?t=8090
You can click the three dot menu next to the share button to pull up the autogenerated transcript or offical CC on c-span, on youtube. I don't think you can search in the yt app like you can on desktop/mobile. The comments section there speaks volumes about the divide between those congressman and younger generations.
"The responses can have a variety of causes, from an involuntary reflex reaction to exposure or inexposure to light—in low light conditions a dilated pupil lets more light into the eye—or it may indicate interest in the subject of attention or arousal, sexual stimulation,[3] uncertainty,[4] decision conflict,[5] errors,[6] physical activity[7] or increasing cognitive load[8] or demand."
https://en.wikipedia.org/wiki/Pupillary_response
https://www.microsoft.com/en-us/research/wp-content/uploads/...