Connecting this with the tomato plants, I called poison control and asked if eating a single plant, about an inch tall, would hurt him at all. Especially since he'd probably eaten it last night, would there be delayed affects? None of the BIG seedlings were missing, just one of the small ones.
Turns out that there is a delayed reaction, anywhere from 3-24 hours, so that fits. Eating only a single plant shouldn't cause anything more than a stomach ache. If he'd made himself a whole tomato plant salad, there might be vomiting and diarreha, and possibly a lowered heart rate if he'd eaten a tenth of his body weight in the stuff. Luckily, most of the plants are still entirely intact, so I don't think he did that, and I don't think Jet's in any danger, he's just possibly going to be uncomfortable for a while.
The plants are all now well out of reach. And it may even not be the plants, he may well just have some stomach flu or something else entirely. We'll see.
I sometimes think that the most maddening things about being a parent are the complete mysteries...