althought not the sname snake, i have carpet pythons that do it sometimes also. sometimes they will strike,constrict then eat and sometimes they will just prefer me to lay it down and let them eat it. all of mine eat the proper size food and still do it so i agree it isnt an issue of food size. i just think sometimes they become lazy or something lol. i have noticed though if you thaw them then let them warm up to room tempurature or a little warmer they will stike more often. but if unthawed and not 70 to 80 degrees in tempurature they will just eat it like they know its already dead.