Well, I've had an interesting afternoon with Sleipy.
First, I decided to become aggressive with a fiddler. Not only did I dangle it in front of his den, but I pretty much forced it inside with my finger and wouldn't let it leave. Sleipner didn't seem to care. At one point the fiddler even wedged himself between the octopus and the side of the pipe. I've noticed Sleipner has a couple white spots on him similar to the ones that would appear on my cuttles from time to time. Perhaps they're damaged iridiphores from a crab pinch? Its consistent with why he doesn't like to go after crabs, and why he's a little sheepish even when he has.
I was worried that this might stress him out a little bit, but after the ordeal ended Sleipner came back to the front of the den to peer out again. I let him relax about a half hour or so while I thawed some krill.
I worked the krill against his medial suckers using the feeding stick, and decided to stick with it (har har) even after he tried to blow it away. Sometimes he gives an ambiguous response: he will move his body so the piece of shrimp is pressed against him near his mouth: you could argue he's trying to push it out of his den or trying to engulf it but is thrown off by the stick. Sometimes while doing this he will leave his den almost completely.
I tried using my fingers instead of the stick and had a little bit better luck. He took a piece of krill, reoriented it a few times and nibbled on it for a couple minutes before spitting it out. You could see that the face and eyes had been sliced up by his beak. If he had been chewing on the more tasty end of the shrimp perhaps he would have kept it? I'll try again tomorrow. This entire action didn't seem to phase him at all either--he did nothing to slink far back into his den, blow water, turn white or ink. It was almost like playing.
After he rejected the shrimp I tried giving him a snail by hand, but that was the point he pulled an empty shell in the front of the den to say "enough." I think he does trust me to some extent because the shell isn't very big and doesn't really offer any cover; whereas he could easily grab a couple big shells and block most of it off.