So Mrs Slade took him along to a special pool at St Andrew's Farm Kennels in West Sussex.
Feline fun
Most cats hate water, but far from trying to claw his way out of the pool, Custard splashed around without so much as a hiss.
In fact, according Mrs Slade, he loves it. "He lets out a miaow when he first gets in and then happily swims around for 15 minutes."
After 14 sessions in the pool, the muscles in Custard's back legs are much stronger.
Now he can jump onto tables - and before long, he'll be catching mice and chasing birds like all his other feline friends!
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