You have a problem when you find your cats interested in your food - in this case, lettuce. Normally, we could finish a stalk of live lettuce without much trouble even when shared with the guinea pigs (when they were with us). These days, a stalk like this lasts 2 days when mixed with Tuscan cabbage and Kale. I think the cats like the smell of lettuce - at least this sort. It probably reminds them of cat grass.