Not sure there's anything much to add to this.
Mums usually take care of the placenta themselves here. I haven't had one reject them yet. I like to break the cord with my (clean) thumbnail myself - I get paranoid when I see mum chomping on the cord up close to baby's belly.

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Beautiful Bengal Kittens from Dollycats
Beautiful Savannah Kittens from Teardrops Savannahs