Loki smiled, the kid did seem to genuinely like Sleipnir. He didn't know if Hermod knew the details, he didn't know if anyone actually knew the details. There was suspicion, of course, when after the incident with the wall, Loki finally showed back up months upon months later with a colt in tow. An eight-legged colt. But as far as Loki knew, the only individuals that had formal confirmation that he had carried and birthed the animal were Odin and his horse-faced wife, Frigg.
Moving closer, he nodded in agreement. “It will be as if my lips were sewn shut.” He probably wouldn't have mentioned it to Odin anyway, not having thought it was anything out of the ordinary. Sleipnir was a horse, Odin's now, and Hermod was Odin's son. It made perfect sense to him. As long as Loki's son was being treated well, he had no business tattling or being possessive.
When he stood in front of his son, who was looking at the apple Loki kept tossing in the air and catching with fascination, occasionally nickering in desire for the apple, Loki chuckled. “Want this, eh?”
Loki's hand reached out and laid one hand on Sleipnir's forehead to calm him, the other bringing the apple down to his muzzle for his mouth to find. Which didn't take long. In a few frothy bites, the apple was gone and the Trickster stood there, just stroking the forehead and muzzle of the beast.