This one happened over the summer, so I'll add it now - death by injury/diet.
I had a 6 inch maxi mini eat a 3 inch horseshoe crab. Head first. The tail was the only thing I could see sticking out, and with all the spikes pointed back there was no way it was coming out. I gave the anemone time, hoping it would figure something out but it died with the crab still in it.