Stuck in a metapod costume

[Hypercat-Z]

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So Belly Bear decided to going to a halloween party costumed as a butterfree. But then Plain Greyhound sugested her to turn her costume better by hiding it into a Metapod costume.
Unaware of Plain's plane Belly accepted and letted her take care of it. Though she should have got a clue when Plain sealed her mouth and immobilized her arms and leg.
Only when they reached the party and everyone complimented Plain for her job, without her mentioning anything about the other costume inside, Belly guessed she had been deceived but she couldn't do anything but squirming and moaning in her, unable to enjoy the food and, most important, impossibilitated to harass the guys.