How to respond?

So my boyfriend asked me what I think when he gets boners. I honestly don't care and think it's just a natural thing but I think he wants a slightly more exciting answer than that. He gets them when we make out or if I'm just wearing something that he likes. We don't do anything more than just making out and I don't intend to till I'm older so how should I respond? (He does know I'm not interested in going any further rn)
How to respond?
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