A bunch of heroes were bleeding. After resolving an action other than taking the action to remove it, you take a strain.
If you have stain=endurance it converts to damage
You cannot intentionally take take strain that would cause damage. "A hero cannot choose to suffer (strain) if the amount of (strain) he has suffered would exceed his Endurance. This includes suffering (strain) to gain movement points or using abilities with a (strain) cost."
So effectively if you're full on strain you can only take the rest action (and consequently have endurance left when the bleed would kick in.) or remove the bleed. If you do anything else you are choosing to take a strain in excess of endurance.
However, its not explicitly a (strain) to do X. Where is the line between choice and game effect? My thought if you perform and action that will result in you 100% taking strain, you are choosing to suffer it no matter the source. If its merely a possibility (like you have to roll a die for an attribute test and take strain if you fail) it would be allowed.