From Vern Lefever:

Re: From oral to moral? Dirty deeds may prompt “bad taste” reaction (Feb. 27): Interesting that the wrinkled nose is singled out, over the years I have found that very young babies will respond to nose wrinkling with smiling eyes and mouth with laughter. The same response comes from kids up three four if they are open an unconditioned at the moment.

Seems like the closing eyes and scowling mouth are needed for the negative response.