Maybe I'm imagining things but I think I can see some teeth or bill markings on the inside flesh of the tomato - nibble marks left behind by your culprit. This may help to narrow the field. Mouse, squirrel, rat or bird?

Teresa

or neighbor, LOL

My first thought after looking at the picture was slugs...then you said the tomato was on the ground and that you are having problems with snails. I'm guessing your problem is still the snails.

Shaila

I think it's a rat. I saw someone duck under the foliage a few days ago and it wasn't Mr. Snake.

Provide a pan or two of water in the area and see if it stops...usually works for mammalian nibblers.

What's the function of water? Mr. Rat is thirsty? What if he's hungry? A sandwich? (Sorry, I feel sort of giddy this morning.)

I read somewhere you chop up some cork and mix it with bacon grease. They eat that and morte.

The dogs usually have a bowl of water near by
but if it worked Id try it
heck they do get thirsty eatind a half pound of my Missouri Pink Luv Apple tomatos and testing all the cherry tomatoes

Squirrels often take a bit and then move on. They also don't seem to care whether the tomatoes are ripe or not--just chomp, and move on.