Dr. Free-Ride: So, you know how sometimes you have nightmares?
Younger Offspring: Yeah.
Dr. Free-Ride: I had a nightmare the other night.*
Younger Offspring: What was it?
Dr. Free-Ride: Well, I was supposed to be picking up snakes with two sticks and moving them from one place to another.
Younger Offspring: Why?
Dr. Free-Ride: I don't know why. It was one of those dreams where, in the middle of it, you really don't know why it is like it is, but you just go with it. But anyway, it was fine until I realized that one of the snakes that I had to pick up was a cobra.
Younger Offspring: Yikes!
Dr. Free-Ride: And how I realized that was that its hood was all spread and it was making that move it makes before it strikes. So I decided I wasn't going to pick it up, and I turned around and went the other way, and I woke up when, in the dream, I thought I felt its teeth on my calf.
Younger Offspring: Eeek!
Dr. Free-Ride: But here's the thing, after I woke up --
Younger Offspring: Was it in the morning, or in the middle of the night?
Dr. Free-Ride: Early, early morning. Too early to just wake up. But I thought of something before I fell back asleep.
Younger Offspring: What?
Dr. Free-Ride: Well, you know about cobras.
Younger Offspring: Yeah, they're poisonous. Did you think a cobra actually came in the house?
Dr. Free-Ride: No, I knew it was actually a dream by the time I woke up. What I thought to myself, as I was falling back asleep, was, how come poisonous snakes don't get poisoned themselves when they eat the things they've bitten?
Younger Offspring: Why don't they?
Dr. Free-Ride: Well, after I woke up for real, I did a little poking around to try to find out. One thing I found out is that the venom that most poisonous snakes have, that they use on their prey, isn't venom that would poison you if you swallowed it. It harms your body if it goes into your bloodstream directly, but not so much by way of your stomach.
Younger Offspring: So if a snake bit itself, the venom could hurt the snake it came from?
Dr. Free-Ride: That's what it sounds like from some of the stuff I read.
Younger Offspring: Well, then I wish that cobra in your dream would bite its own tail.
Dr. Free-Ride: You know, I have no problem with dream cobras. As long as they don't come back.
Younger Offspring: Yeah.
Dr. Free-Ride: So, I had pretty much found the answer to my question about why snakes don't get poisoned by the prey that they eat after biting it. But then I kept reading around and discovered that some of the people who study snakes think there's an interesting question about why snakes might have evolved venom in the first place.
Younger Offspring: Don't they use it to kill their prey?
Dr. Free-Ride: Or immobilize it or whatever? Yeah, that seemed pretty reasonable to me. But I guess that it turns out that some snakes with venom are also constrictors -- so they also squeeze their prey. And some scientists have wondered why a snake that already has a pretty good way to kill or immobilize its prey would also need venom.
Younger Offspring: Yeah, why?
Dr. Free-Ride: Well, some scientists have guessed that maybe something about the venom helps the snakes to digest the prey that they've bitten.
Younger Offspring: So, if a snake drooled on its prey, would it be drooling venom?
Dr. Free-Ride: I do not know. If it were, I suppose it would need to drool on an open cut to be effective. To be honest, I don't know whether snakes drool at all, let alone whether they drool venom.
Younger Offspring: Maybe the scientists who study snakes know that.
Dr. Free-Ride: That's who I'd ask. Anyway, as I was reading that it was a question of how exactly being venomous helps snakes, I found a cool paper about research scientists tried to do to figure out whether venom helps snakes digest their prey.
Younger Offspring: Maybe for the next science fair I could do a project on it.
Dr. Free-Ride: How would you do a project on it? That would be an interesting question.
Younger Offspring: I'd have to be really careful with it. And you'd have to help me.
Dr. Free-Ride: Kiddo, I am not committing to bringing poisonous snakes into our home.** Right now we're just talking about how we might be able to answer the question.
Younger Offspring: OK.
Dr. Free-Ride: So, if we're talking about a snake that eats mice, what could we do to find out whether it's digesting the mice faster or slower if they have venom in their bloodstream?
Younger Offspring: Hmmm.
Dr. Free-Ride: Well, how do you tell whether you're digesting something fast or slow? What are the things you could observe that might tell you?
Younger Offspring: That if I'm eating something fast, my stomach will hurt after that.
Dr. Free-Ride: Hmm, how your stomach feels.
Younger Offspring: I can also taste more flavor if I slow down when I'm eating.
Dr. Free-Ride: That's more about consuming fast or slow. But digesting is after the consuming, isn't it? Where does digestion happen? It doesn't all happen in your mouth.
Younger Offspring: In your stomach. And intestines.
Dr. Free-Ride: So how do you tell if you've taken a short time or a long time to digest something?
Younger Offspring: If I've taken a long time, I won't need to go to the bathroom for a long time.
Dr. Free-Ride: Mmm-hmm. And this is one of the things that the people studying the snakes to answer this question did to track how quickly the snakes were digesting their prey.
Younger Offspring: They timed how long it was before the snakes pooped?
Dr. Free-Ride: Pretty much.
Younger Offspring: And you found out the scientists were studying this because you had a bad dream.
*We are, apparently, no longer at the point where it's surprising that grown-ups dream
**Actually, we've discussed why we just might not be snake people.
Younger Offspring is going to grow up with a wonderful understanding of how to think scientifically. Will not be easily fooled. A science-ninja, as it were.
Snakes do drool.
Well, at least they salivate. So do lizards. Snake venom is modified saliva, and venom glands are modified salivary glands, and if they aroused/hungry you can see the strands of venom/saliva in their gape.
Got a snake for you if you want a harmless slightly venomous snake that uses it's venom to digest. A hognose. You can now get these snakes through breeders and though they prefer to eat frogs/toads (and some species will only eat this), some of them will accept pinky mice. They are a very easy going snake, small, and you can't get envenomed because it's a rear fanged snake. You would have to shove your hand down its throat and even then, it won't kill you. Though I understand your hand will swell up.
Oh, heard something else about snake digestion. Apparently, you can feed a snake cooked food and it will stay full for longer. I can't find the paper on this, but it was showing how cooking aids in digestion.
Take that back, got the paper. http://www.ncbi.nlm.nih.gov/pubmed/17827047
Apparently, Komodo dragons actually *do* drool venom.
(Perhaps the kid shouldn't be told until he's old enough to wrestle them, though.)
It is my understanding that saliva has lytic enzymes to remove food debris from the teeth, this is why humans have amylase in their saliva (which is inactivated at the pH of the stomach) and carnivores have proteases (off hand I can think of cats (the major cat antigen people are allergic to is a protease in their saliva) and walrus). One of the reasons that carnivore bites are so difficult to heal is because of the immunogenic effects of the proteases in the saliva.
What would be interesting is if the lytic enzymes in saliva change over the course of an organism's life, for example some lizards (iguana I think) are carnivores when young and become herbivores as adults. Do the lytic enzymes in their saliva change?