I would definitely want to address this with my vet. Both of my boys are neutered and I know humping is natural and happens but I have never heard of a male penetrating another male and ejaculating. Has ANYONE ever heard of this? Maybe I'm just sheltered.
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"If you have men who will exclude any of God’s creatures from the shelter of compassion and pity, you will have men who will deal likewise with their fellow men." — St. Francis of Assisi, 1181-1226