This is especially noticable if you have Speed II and walk backwards and pull a baby snifflet on a lead, but can also happen if a water stream is pushing a sniffer.

Steps to reproduce

1. Spawn a snifflet.
2. Drink Speed II potion
3. Lead the sniffer
4. Walk backwards.

The sniffer walking animation plays but extremely fast, causing them to appear to vibrate. They also kind of wiggle/face away from you which might be a separate bug but I'm not entirely sure.

Possibly caused by the animation speed being proportional to the walking speed, but since the game doesn't expect sniffers to be able to move that fast, it causes the animation to play way faster than it should.

Video: https://www.youtube.com/watch?v=sEOcACZa62w