I’ve seen this photo several times, but every time I’ve seen it, the left-hand side was always cut off.
Now that I see the full photo, you can see what was going here.
Someone wanted to introduce his spaniel (an English springer, by my estimation) to a captive thylacine.
I guess this would be the equivalent of a human meeting a Klingon or a Vulcan for the first time.
“You’re similar, but you’re not the same!”