> >un tigre, dos tigres, tres tigres
> This is a tongue-twister? Admittedly, I *cannot* say it fast, in that I
> cannot say anything in Spanish fast, though the 'strest' of '~s tres
> might present a problem.
> Now: "better rubber baby buggy bumpers" sends you into lip-spasm.
> Even better: Pope Sixtus VI's 6th sick-sex text's texture (this cannot be
> said fast at all).
Well, it's played by children, and may be is the shorter one.
I think that one can fail even in the second "tiger" that way:

< un tigre, dos trigues... >

(the < u > of <gue> is ortographic and does not have sound).

in the third tiger one can fail in several ways:

<..., tres trigues >

<..., tres tigues >

<..., tes tigues >

<..., tres trigres>

or other ways.

Your second tongue-twister, yes, really a hard one.