I do not believe you have said what type of corns these are,some corns especially those with miami backgrounds are reported to prefer lizards and can be quite difficult to change!If you can, assist feeding a mouse tail cut to around the size of the hatchling to be fed works well.Pry the mouth of the snake open a bit (a long finger nail works well)and force the tail into the mouth and throat of the snake, not far just a millimeter or so.The snake will then either try to shake the tail out or start swallowing the tail,if it trys to shake it out,usually just touching the tail of the snake will cause it to try to get away and in wanting to go forward it will usually stop trying to shake the tail out and begin to swallow the tail.This is Very stressful, and it may take a time or two to get it right.I would strongly suggest that once you accomplish a feeding this way to leave the snake alone for a few days.And I would also caution you that there are some snakes that just can not be saved!Good Luck! Let us all know how it goes.