It could be that the stag's tooth replaces the pebble that many hikers will put in their mouths as a salivary stimulant to forestall thirst. The word "gristle" is curious. An author can use the word to create a mood; after all, there are probably no light, upbeat scenes in literature that incorporate the word gristle. Or - and I'm shooting from the hip here - it may be that, before the introduction into Europe of chicle from Central America, it was customary in some areas to dissolve the calcium from animal teeth and use the remaining gristle-like matrix as a thing to chew. Pure guesswork, as I've never heard of such a practice

"I don't know which is worse: ignorance or apathy. And, frankly, I don't care." - Anonymous