Since your 2005 furby used to work fine, but now cuts off mid-sentence, the connection has a problem. Sometimes the battery compartment/cover crack and break over time, since you have to manually screw it in. You can always buy a new replacement cover online. Like this one: https://www.etsy.com/listing/1209305021/resin-battery-cover-for-emoto-tronic
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So I would check to see if all the battery terminals are making a connection. Check for corrosion, if the batteries corroded recently, it could be the problem, and you may have to clean it. You can also reset these Furbys, hold down the tongue of the furby, and turn them off and on, this could help fix the problem. Here is a video showing how: https://youtu.be/SjOP8gH6mCE
I am only concerned about it getting stuck and whistling, the whistling could be the motor humming and the gears could be stuck, meaning you'd have to take the furby apart to lubricate the gears, when it gets stuck try moving the ears, beak, and feet. This may move some of the gears internally and get the furby to move again. If you need any further help you can always contact me at Oliviarepairs@gmail.com or my Youtube channel: Olivia Furby Repairs
I hope this helps, Thanks!