As heartmountain mentioned, the only time I have heard vegetable or mineral oil used with dragons is to help with constipation or minor impactions. I wouldn't recommend it being used on a dailly salad. Other ways to entice your dragon to eat their salad is to offer it first in the morning and don't offer any insects at all, except for maybe a couple a few hours later or in the later afternoon instead. Or you can drop a few insects into the salad, such as silkworms or superworms, let them have a chance to work themselves underneath the greens or cover them up. Your dragon may be more inclined to dig through teh salad to get at the insects and inadvertantly eat greens as welll. He may then decide he actually does like them. If he is every good at getting the bugs but no greens, cutting the greens smaller could ensure more stick to the insects, or not giving any insects till later on in the day or only a few times a week.
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PHLdyPayne