The homoeroticism between Laurence and Temeraire, if you'd like to see it that way. Case in point: Laurence calls Temeraire "my dear" and cuddles him a lot, as well as mentioning how he can't see how any dragon captain could marry and divide their affections between dragon and spouse. Also Temeraire going through puberty and Laurence touching the wrong part of Temeraire:
"Come now, you are like to make everyone think you are a vain creature," Laurence said, reaching up to pet the waving tendrils. "Truly, they look very well; pray give them no thought."
Temeraire made a small, startled noise, and leaned in towards the stroking. "That feels strange," he said.
"Am I hurting you? Are they so tender?" ...
Temeraire nudged him a little and said, "No, they do not hurt at all. Pray do it again?" When Laurence very carefully resumed the stroking, Temeraire made an odd purring sort of sound, and abruptly shivered all over. "I think I quite like it," he added, his eyes growing unfocused and heavy-lidded.
- Laurence's reaction to this statement, however, is to immediately recoil away and attempt to explain to Temeraire why he stopped.