It is a safe treat, but not a good treat. High in sodium, and a lot of dogs can be allergic to the ingredients in the cracker, so giving it to him regularly may cause him to itch. Some better treat ideas are apple slices or carrots or green beans, my dogs love them, and they are good for them as well.
I'm not sure it would hurt them... unless they have allergies. But this type of treat will not benefit them either. I tend to lean towards carrots, chunks of chicken, even cheese as these have ingredients that are better for them.
I also don't really like to feed dogs while I am eating mainly because then they can develope a habit of begging (I especially will not do this if they are a foster because it wouldn't be fair to a new family who may not want to continue this habit).
I would suggest making them show off and do tricks/challenges first and then give them the people food as a reward.
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Maybe just alittle would not hurt. Mandy loves Cheezits but I'm sure they have alot of salt. They all love Graham crackers. I mostly for snacks give them baby carrots, apple. They also love cottage cheese and cantlope.