This is a hidden gem of a horror film, a 2009 movie (also from director Joe Dante of "Gremlins") that captures the feel of the great '80s PG-13 horror movies. There's innocence and terror as the main characters (all kids) find a mysterious trapdoor covering a hole with no discernible bottom.
It takes the kids a while to figure out the hole is bad news, but their dog Charlie knows right away. This sets up some goofy, kid-style double entendres like, "Charlie doesn't like your hole very much." Unlocking the hole unleashes some kind of horrific entity, but Charlie is never harmed. Like many supporting actors, he doesn't appear on-screen in the second half of the movie, so we can assume he got bored with the trapdoor and went off to do more sensible dog things, like digging his own holes and napping.