When I was very young, my parents GSD had to have a major operation (this was round about 1980 or so) to remove an entire ball of wool from his stomach. God alone knows how, or even why he felt the need to eat it, but... other than the surgical wound and resulting scar, he was fine. The vet apparently offered the still wound ball back to my parents (who said "thanks, but no thanks!").
My 13 year old Springer is a nightmare for eating things he shouldn't. Particularly from my daughter's room - he's especially fond of unused, still in their wrapper, sanitary towels, so we have to make sure they're in a drawer he can't open (I think he likes the floral scent of them, quite frankly). At the moment he's totally off his food, and I'm trying to work out how to get the floral scent of the towel wrappers onto his specially prepared meals in an effort to tempt him (and, to be honest, I'm only half-joking: he's my 14 year old son's best friend, and it's his birthday on Monday, so I'd really rather said dog improves before then. I do have a suspicion, though, that this time he won't
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When I was my son's age, I had a GSD/Lab cross whose stomach must have been made of cast iron! He ate socks, hair scrunchies (he'd literally steal them out of my hair by lying on the chair behind me, waiting until I was engrossed in a book or the TV, then help himself - my parents used to watch him do it, and they always passed through whole after a day or so...).
My other dog, now, though, is prone to knickers. Specifically my 23 year old daughter's nylon lace thongs. The lacier, the better. She doesn't eat them, though - she delicately nibbles one half of the leg bit away, then hides them under her cushion in my room or, even better, under the dirty washing pile where she also stashes her collection of bones. My daughter didn't believe me when I said it was the pup and not the washing machine ripping her (expensive) undies apart, until she caught her mid-nibble one night. I think the dog likes the nylon scratchy lace and uses it to floss with, because her teeth are pretty much see-in-the-dark white...
I'd like to say that they grow out of it, but once they get into the habit of it, and work out that there's attention attached - even if it's bad attention of their owners shouting/crying/begging to know why they do it - they carry on. They're slightly like permanent toddlers in that respect (both of mine used to eat weird things, too!).