Foxtail seeds are very tiny so veterinarians usually go by symptoms.

If in nasal cavity, dog sneezes repeatedly and violently often hitting nose on floor. If a bloody discharge is noticed assume it's a foxtail seed.

If in eye, dog paws at eye and eye waters. If an eye is glued shut it is most likely a foxtail seed.

If seed is in ear dog shakes its head violently from side to side. Sometimes dog paws a eyes or ear, shaking head and squints.

In mouth foxtail seeds can cause gagging or difficulty swallowing. If seed gets caught between teeth, in gums, back of throat, or tongue problems can result.

If seed lodges in paw or under coat a lump will form that is painful to touch. Other symptoms include rubbing head on ground and going round in circles, licking or biting at rectum or other body parts, or yelping or shining for no obvious reason.

Foxtail seeds can cause fatalities when they reach internal organs.

In any case, do not attempt to treat animal yourself. Get professional help.

Get rid of all foxtail in your lawn or yard. If foxtail grows in your yard mow grass often, especially in late spring when plant grows most rapidly. This prevents plant from ever setting seed.

Avoid parks, or other recreational areas where you know foxtail grows.

Always brush and inspect your dogs coat after being in grassy areas. Dogs with long hair are even more likely to attract seeds than shorthaired breeds.

Examine your dogs eyes and ears.

For more information on how to control foxtail:

http://www.apluswriting.net/garden/foxtails.htm