In the mid-credits scene of Thor: The Dark World where Sif and Vostagg go to see the Collector, the image above can be seen. It wasn’t clear right away but after a little research (reading comics) it reminded me of the cocoon that Adam Warlock has been known to emerge from. In case you were wondering, he creates a cocoon for self-preservation and regeneration.
Adam Warlock is a key figure to Thanos in the comics. Check the images below and judge for yourself.