Here's a short clip showing Suárez apparently trying to bite his own Liverpool teammate, who was celebrating after a goal. When did this happen? Do we know any additional context that would explain what Suárez was doing and why he was trying to do it?
EDIT: I think @Ben is right. Suárez is trying to slide on his knees and failing. Momentum keeps his upper body moving forward even when his lower body has ground to a halt. His mouth is probably open because he's yelling (happily).