Only gonna post the link to youtube rather than the full clip on show so it dont scare people lol (if old 80's movie makeup effects do that to ya) but its the deformed dog from the movie The Fly 2.
That shit has haunted me since i saw it as a kid and still does, fuckers because everytime its on i have to switch over that scene till its finished.
https://www.youtube.com/watch?v=HAFXgJKJpn4
...and the other scene just to add where he puts it to sleep but i didnt bother looking for that on youtube thank you very much.