Panda cub is adorably sleepy at the Toronto Zoo
Twin panda cubs are now 12 weeks old and teething
In case you thought the idea of cute cubs at the Toronto Zoo had grown tired ... one of them yawns.
Zoo staff today released a video of the adorably tired twin cub yawning.
Toronto Zoo's twin panda cubs hang with mom Er Shun in new video
Toronto Zoo panda cubs outgrow their incubator, are somehow even more adorable
Twin panda cubs begin to open their adorable eyes at Toronto Zoo 
The pandas are now 12-weeks-old and weigh more than 3.5 kilograms. The zoo says the cubs are getting stronger by the day and are beginning the teething process.
The cubs are in the zoo's maternity den and not available for viewing by the public.
The twin cubs were the first-ever giant pandas born in Canada. Their mom Er Shun is one of two pandas on loan from China.
All of the pandas will be at the Toronto Zoo until 2018, when they'll move to the Calgary Zoo for five years.