If it was me, and I had the slightest thought it was a snake bite, ie, I had seen a lot of snakes around lately, area is known for snakes etc, I'd be going to the vet pronto just to be sure, because it may be to late once you start to see 'symptoms'. Check to see if you can see puncture wounds ?
I once seen one of my cats out in a sugar cane field, young short cane, and by her actions she was obviously doing battle with a snake, was about 100 m away, I didn't know whether to grab a shovel and race out or what, my thinking was that if I went running over, it may distract her, taking her attention away, and that would give the snake a free shot, same thing with calling her, just didn't know what to do, it all ended well though.