[Unsurprisingly, that kiss to their head gets them to squeeze their eyes shut for a second, before they look over their shoulder to blink up at her where she stands on that stepstool.]

... This strange little thing which you keep doing to me with your mouth - that is a kiss, correct?
What is the purpose of them? I have seen others do this many times, but I have not yet seen a common reason behind it...

[They've seen friends greet each other with kisses, they've seen parents kiss their children, they've seen couples kissing under streetlamps... there's nothing linking all of these things together, as far as they can tell!!
(Yes, there is. Purple just can't see it very well, not having experienced love much themself.)]

... Is it because you believe me to be sweet?