My Dog Came Across A Large Caterpillar With A Thorn Looking Stinger Hanging Out Of Its Back, It Looked Like It Had Two Fangs At The Front, Its Head Is Large And It Follows You Round When You Look At It?

I found the same thing yesterday eating my Datura plant. The leaves were completely chewed off. When I looked closer to inspect the plant, I saw this caterpillar/larvae. It was chewing on a leaf. I swear that it stopped chewing and looked at me when I leaned in to get a closer look. (My husband thought I was crazy.) He poked it with a stick, and it actually attacked the stick! It was quite comical.
Anyway, I looked it up and mine was a tobacco hornworn which they say is often confused with a tomato hornworn. They do look similar. They turn into these huge brown moths.
By the way Datura is poisonous, and caterpillars eat it to make themselves poisonous. Interesting.