Thread: How clean is a clean kill?

Hi all,
Relative newbie here. I got my first half-serious air rifle last week and shot its first possum with it last night down the back of our section. First time with my own equipment, after having shot maybe a dozen or so using friends ruger 10/22's.

Last night there was a delay of probably a 10-15 seconds(?) before it dropped from the tree. So long that I was about to place a second shot by the time it did drop. I then searched for it for probably 10-15 minutes but never saw or heard anything from the possum and never did find it (though it's a very challenging bank with dense undergrowth and not even sure i'm looking in the right place)

1) What kinds of times are you typically seeing between impact and a possum dropping?
2) Is it possible I just winged it and it dropped the full 20+ meters to the ground and then hid or snuck away in near perfect silence? I would really like to think the shot went where I aimed it, and the delay was just how long it took to bleed out and lose consciousness / fall.

Targeted area: Front chest/neck, unconfirmed it actually hit here.
Ammo: Winchester domed pellets, unknown weight.
Rifle: Gamo Whisper wildcat. Stated energy 17.7 fl.lbs / 24J.
Distance - 20-25 meters? shooting at 70 degrees up.

Trying again in the same spot tonight. I really want to make sure these are clean kills, and adjust things as necessary if not.