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Since the only real symptom is a touch of hyperactivity. you will need to see if there is any poisonous plants or trees in the yard. Some can cause hyperactivity. Usually you see vomiting, nausea and diarrhea with poisoning but not always.
I have also seen this behavior from my dogs when they have been stung by a bee. The initial sting scares them a little and they often want to be with the owner but are leary of everything. Some will avoid sitting down if they were stung on the rear. It is also likely that the sniffing was to try and assure themselves that the offending bug wasn't in the house. Often there will be a localized swelling at the sting site.
If you suspect he may have been stung, you can give benadryl at a dosage of 1mg-2mg per pound every 8 hours to help with allergic reactions. Read more on insect stings and bites here:
If you do have toxic plants or trees in the yard, let me know.
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