nope..you can't tell what snakes ate by looking in the feces. scales will digest...known fact from wandering eating lizards....looked just like any other poop...on rare occasions, mouse fur will pass, but generally everything digests. garters are master escape artists. it would be hard for one to eat one near the same size, unable to the the whole thing ingested. snakes can outdo Houdini!!! I know of a 6 ft red tail boa that squeezed out of a cage with the widest gap only an inch and a half....happened at my work. the snake was big and stocky, didn't think it could squeeze out. babies also can get up the side of aquariums....they crawl thru the water dish and get wet, then stick to the side of the glass....had that happen to me....