that cocoon is lethally trapped....
The only thing you can do, is as you click on the cocoon, press spacebar (have plenty decent healing potions available). drink one, and quickly press the spacebar twice (split second unpause), drink another healing potion again, even if you are not close to death, since you dont know how much will go down in the next split second unpause...
repeat this for a few times (most of the trapped things i have opened, took me about 8 - 10 repeats of this "split second" unpause.
Its a littlebit of a waste of potions, but its one way not to die....
