Anna and Nora are playing Modern. Nora is playing Scapeshift, Anna is playing dredge. Nora's board is 8 tapped lands and 1 primeval titan.

on Anna's turn she taps 2 mana, says “Life from the loam” then says wait before Nora does anything. Is Anna obligated to cast and resolve Life from the loam?

It sounds like Anna corrected herself immediately, she was not fishing for information, and it reads like Nora didn't have many ways to interact anyway. Also, Anna didn't cast Loam yet, as that card requires targets. I see no problem in Anna correcting herself here; let's continue the game, and remind Anna to be slightly more careful in the future!

I generally agree with Dustin, but have to point out that this is very much a “you had to be there” scenario.

From your description, Brock, Anna didn't even put the physical card “on the stack” (i.e., she didn't even show the card, much less move it from her hand to the table or something similar)? and she stopped herself immediately, before Nora could react - thus, before Anna could gain info from a reaction.

I would do a quick investigation, to confirm what Dustin and I are assuming from your description, and then rule accordingly.

d:^D