I can just tell you that when I was 16 the only kiss I had ever gotten was on the cheek. Similar was the case with most of my friends back then. So I don't have any problem believing that, infact it is more relatable to me.
For Sam this could be a once in a lifetime kiss for him with Sophia, the woman he desires. Will he really care about his inadequacies. He will do everything he has heard or seen. French kisses are common these days. Similarly popularized are kisses on the neck. So a teen of his age who has seen all of this will try it definitely. That's how I see it. It was never said that Sam is an expert kisser either. So it's all about doing whatever he can. His other actions also support this notion as he tries to fondle her, kiss her all over, suck on her breasts. He tried to do everything he could. Which to me is the most normal thing a teen would do when given an opportunity like this with his most desired woman.
What will happen in the next scene will decide whether it will be logical or not. As of now I am just happy that the fear of almost being caught made her wish she never did any of it. Which was realistic to me.
The edge was quite thick honestly, there is seating space plus the thickness of the tub. Sam was beyond that and stuck as close as possible to Sophia as well, he had to keep his head low anyways, plus you are playing a erotic novel ofcourse if his head is there he will try something. Add to that that Liam's view was completely blocked and as he is released from the kiss he was immediately pushed back to get the phone
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There is no way for Liam to see anything here
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This render is an in motion render whose description says that Sophia "pushes away Liam and tells him to get her phone" thereby not giving Liam time to look in the tub, as the kiss breaks he is sent away, if this were in a video format might have been much easier to accept I believe, plus no reason to suspect any person inside the tub, also refraction could be playing an additional factor, and Sophia hurrying him to get her phone. I can easily accept this and not make a huge deal out of it.