Fourth Wall

Sometimes in Happy Tree Friends, something will happen that implies the characters are aware of being fictional characters in a cartoon. This is known as breaking the Fourth Wall. The term "fourth wall" originated from plays in theaters, when actors would look at the audience, talk to them, or do anything else that involved the audience. Because the stage would generally have a wall at the back and both sides, this concept involves the actors becoming involved with the audience who are at the front, which can be considered an invisible wall, making it the fourth one. The Fourth Wall is most often broken in smoochies, but has also been broken in TV episodes.

In Smoochies
Pet Smoochie: Cuddles waves at the viewer and says "Hello! h-h-he, h-h-he".

Valentine Smoochie: Giggles blows a kiss at the viewer(s).

Baseball Smoochie: Flaky waves and chuckles nervously to the stranger that's watching her.

BBQ Smoochie: Pop waves his hat and says "Hello there!".

Olympic Smoochie: Mime shows off his strength by pulling an invisible rope.

Halloween Smoochie: Disco Bear dances for the viewer(s).

In TV Episodes
And the Kitchen Sink: When Pop's car lands in the water, it makes a big splash, it can be seen that there is water on the screen sliding and dripping down.

Party Animal: At the end, the iris closes on Flippy's mouth, cutting off his lips.

Wipe Out: When a wave splashes on Flaky and Cuddles, it can be seen that there is water on the screen sliding and dripping down.

Take a Hike: They hum the HTF theme song at the start of the episode (they also do this in From A to Zoo).

Blast from the Past: Cuddles yells, "Oh my God, I'm gonna die! Not this old death again!" This impies that he knew he died in Spin Fun Knowin' Ya.