You see this happen at least once per year, and there's always nowhere for the guilty party to hide.
This time, it's former Detroit Red Wings forward Jiri Hudler, currently with the Dallas Stars. A delayed penalty against the Ottawa Senators took Stars goalie Kari Lehtonen off the ice for an extra attacker. Hudler took a pass in the neutral zone but immediately swung the puck back, and it slid between the two surprised Dallas defenseman into their own net for a Senators goal.
The goal was credited to Chris Kelly, who was the last Senators player to touch the puck.