I'm just guessing it's just too much food all at once. For my Uni, usually yellow foam is from not eating. If she's still doing it, I would call the vet. Also, greenies say not to give to dogs under 6 months or 5 lbs. That could have been it.
__________________  The T.U.B. Pack! Toto, Uni, & Bindi
RIP Lord Scrappington Montgomery McLimpybottom aka El Lenguo the Handicapped Ninja 10-12-12 
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