Thanks.

I always thought that to stutter/to stammer was the same thing but according to the link below they are different. http://www.nhs.uk/conditions/stammering/Pages/Introduction.aspx To stumble is completely different = Tropezar en algo/contra algo.

Eck, I can't space out that answer in a comment, my apologies for the wall of text!

Stuttering is repeating and or prolonging a syllable or sound, like so: "Th-th-thank you, very mmmuch." It's synonymous with stammering and classified as a speech disorder, and there's several other characteristics to it. Stumbling in speech is 'tripping' over your words, struggling to find the right words or struggling to say the words you have on your mind. It's not a speech disorder, but if you are nervous you might stumble over your words. If 'to stumble' is used on its own, it means to trip or to lose one's balance. In creative writing, stuttering, stammering and stumbling are often used interchangeably to convey the speaker's feelings. Stammering might indicate that the speaker is scared, insecure, startled etc. Stumbling over words is more often used when the speaker tries to say many things at once, or if they speak chaotically. It can also hint at lies being told. I hope this helps!