Bob: "Damn I feel good."
Mark: "Why do you feel so good Bob?"
Bob: "I just screwed a chick with my celtic snake!"
Mark: "Seriously dude you got one of those?"
Bob: "Ya dude I used it on your momlast night."
The feeling of tiredness or sleepiness you get after eating a large amount of food.
Related to the fact after a snake eats a meal it much sleep to digest.