Food Tampering

The humans went to the country cottage again today, and of course a few rabbits hopped along to offer their assistance, and to make plans for more work for me. Does anyone know how to tell if food has been tampered with? The humans stopped at the store to pick up some food for me on the way up, since they feared they might be late getting back, and then they foolishly left this bag unguarded around the bunnies. I noticed a suspicious orange tint to it when it was poured in my dish, and I know some of the bits of kibble weren't shaped like that the last time I had this. I suspect the bunnies of tampering with things, in the hopes of converting me to a vegetarian! But how can I know for sure, and what in the world am I going to do if they did do something to the food? I had just finished the older stuff, so I might be stuck with this, unless I can get the humans to replace it somehow.