The litter test was scrapped. Theo was eating too much of the corn litter! I figured once the corn litter was used it might curb his desire for it, but that was not the case. So, I resorted to mixing the corn with the clay which solved the problem. Hopefully, as we slowly adjust the ratio of clay to corn litter, he will associate it with doing his business rather than having a snack.
Meanwhile, the wheatgrass pellets were continually passed over. Although eventually, Theo became curious and tried them. Like the cats, I can't say I am impressed with the wheatgrass. I suppose it did the job, but it will be used up fast because rather than scooping out just the waste, you have to scoop out the waste and all the litter-pellets surrounding it. And, the when wet, the pellets seem to turn to powder, making it very difficult to scoop out. I can't say I am necessarily disappointed that it will go fast - perhaps not quite fast enough.