I was at an Aquarium today, and saw two Eledone Cirrhosa in a tank. Both appeared initially to be asleep, or at least resting in a (near) motionless state. When some moron tapped on the tank's glass - The one nearest to us began to start moving. One thing that it did, which was just a little unnerving I have to say(!) was to 'wriggle' the tips of all its tentacles rapidly against the pebble/sand floor of the tank, before 'climbing' up the glass wall, then propelling itself rapidly away towards the upper part of the tank. I have a vague recollection that the rapid trembling of the tentacles is meaningful somehow. Is it? And if so, how so?