Apparently the Yeti actors had a difficult time too, because of how bulky their costumes were, they couldnt stablise themselves and also had a tendancy to slip and fall.
I've been up those hills, and yeah, they're SLIPPERY! I sympathise with Deborah here, but I feel more sorry for the guys in the yeti costumes. They slip, and they don't know where they're gonnna land!