Starting car for first time in several months; arcing and turning of an electric motor when reconnecting negative terminal

Ref.
Mazda Tribute, Benzene, V6, 3 litre, Auto-Transmission, 16 Years old approx., 165,000 km approx., 5th Owner

The car has been parked on the street under daily heat from the sun for many months, without being started. I recently tried starting it, however the battery had died, so I replaced it.

The following sequence occurred as I tried reconnecting the new battery:

1. Connected positive terminal to the positive battery post
2. Started to connect the negative terminal to the negative battery post
3. At that moment, arcing occurred between the terminal and the battery post, and some motor (I believe it was in the engine bay) started to turn
4. Immediately retracted the negative terminal from the battery

Note that there was no contact between the negative and positive terminals, so it was not a short.

I have a few questions:

• Did any damage occur from this?
• Perhaps a small animal has shorted the wiring?
• What is the problem happening here?