The dog used to portray the DNA-altered dog is a Tibetan Mastiff.
At least five different dogs were used in filming.
The scene where Max chases the cat up a tree and swallows it, was done in cuts. The dog and cat had been trained together. In the chase down the street, there was always approximately fifteen feet between them. The cat was running to a toy, with food as a reward. The dog was running to visual and hand cues, also with food as a reward. When the cat climbs a tree to escape, he, again, is running after a toy. Trick photography was used where it appears that Max is also climbing the tree. Actually Max was crawling on a log. A fake dog head was used when it appears that Max has the cat in his mouth. The cat had walked in the back end of the fake dog head and out through the mouth. When the cat appears to be swallowed by the dog, it was a trainer off camera pulling the cat backwards through the mouth of the fake dog head.
When Max's eyes are wild and glassy after he is blowtorched, contact lenses were used. The dog wore them for no longer than two minutes.