gag on (something)
To have difficulty swallowing something. I can't possibly swallow a pill that big without gagging on it. Sounds like the cat is gagging on another hairball.
Farlex Dictionary of Idioms. © 2015 Farlex, Inc, all rights reserved.
gag on something
to choke on something; to retch on something. The dog is gagging on whatever you gave her. This fish is good, but I hope I don't gag on a bone.
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs. © 2002 by The McGraw-Hill Companies, Inc.