Snail or slug?

Worm would be the most common problem, and the poop is not always evident when they are small. I don't have a slug or snail problem in my tomato patch...but if most of the damage seems to be near the ground or you've seen them, then that could be the case. I'd spray with BT just in case....and some diatomaceous earth or some slug traps won't hurt anything and are fairly cheap to do yourself.

As for deer...I can't psychoanalyze because we don't have any here in the suburbs.

The way to differentiate between vertebrate pests and invertebrate ones is to look at the size of the stems that are missing. Hornworms will stop when they get to the main leaf stem, and leave it hanging. Deer and rabbits will eat entire branches up to the size of a pencil (at least), and it'll look like someone took a hedge trimmer to the plant. No skeletonized stems left, nothing but clean cuts.

As for why it would be in the center -- who the heck knows, when it comes to deer. Rabbits usually like the outside plants because they want an easy exit, but deer have strange habits.

--Alison