Step 2Un-Suture the Poor Bastards.
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Use the seam ripper to tear through that handy back-seam, pulling out cut threads as you go. If you didn't get an animal with a back-seam, well, shame on you. In this case, I would suggest you make a very neat, straight cut along where the back-seam would be if it had one (down the middle of the toy's back). You don't necessarily need to undo the whole seam, just enough to fit the earpiece of the headphone in. Remember to take care and make it neat, because you're going to have to sew it all back up again in a moment. If your stuffed animal seems ill-at-ease, reassure it with a comforting pat on the head and tell it, in soothing tones, that everything will be all-right.
Repeat for second animal.