"Attracting one’s dragon-mate with shiny ornamentation is just another courtship ritual Sully intends to observe."
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As he is a dragon, even Madrugo has a weakness for sparkly shinies such as gems and precious metals and adding them to his hoard. Sully is crafty and enjoys toying with her dragon so of course she'd have jewels threaded on silver chains for some fancy lingerie to really catch his eye :')
I'm also tickled at the thought of a big mountain of a 'man' like Madrugo being quietly charmed and swayed by something so simple...he is big and scary but he loves his wife.