Younger cat keeps sniffing elderly cat

My younger cat (Duke) has been sniffing around my elderly cat (Clive) who just got back from the hospital the other day.
At first I thougt it was because he knew he returned, but now I find him sniffing around Clive's backside.
Duke is a good boy and has been letting me know when Clive is not feeling well. Can Duke sense Clive's illness? (which is still to be determined)
Also, Clive never really took to Duke, but lately he does not seem to mind his company.
thanks!

Cats recognize each other by scent, so Duke is probably sniffing Clive to smell who he is.

It sounds more like the common phenomenon in which cats come back from the vet smelling like the vet's office, so their companions suddenly have trouble recognizing them.

The smell should wear off in a few days. If you like, you could put some vanilla on both cats so they smell the same... or rub the older cat with a blanket the younger cat has lain on.

makes sense...i will try it! thanks