When we talk about "mechanics", as we often do when talking about games, we often do so at cross purposes. I rarely use the term as a result, preferring something more specific like action or rule, but the fact its that most people don't. At best they often say "action mechanic" or "rule mechanic", and at worst they confuse mechanics with dynamics.
C'est la vie.
One of the useful things I find when thinking of mechanics in small, exacting terms is considering its application beyond games. This question came up on Twitter the other day when Jurie Horneman offhandedly asked whether interactive fiction has mechanics. To which I answer yes.
In game design terms, an action is the application of verbs intended to cause one or more unscripted state changes in the game, like moving an avatar or placing a word. I see no reason why the same can't be said of posting a tweet, or making a choice in an adventure. The other two kinds of verb usage are the same. A nudge, where the player uses verbs to cause a scripted state change, is like flipping the page in Flipboard. A query, where the player uses verbs to find more information about something without causing a state change, is the same as a right click.
Limiting ourselves to only thinking of mechanics in terms of "game" may be a misstep. Often the most delightful actions, nudges and queries are to be found outside of games (Flipboard again) but may have equally fun uses inside them. Why worry about whether they are game mechanics? Worry instead about whether they are worth doing.