Yes it is endemic at MIT. Yes there is an explanation. According
to Jerry Letvin, serveral years ago in his comparative psysiology
class he explained how one sexes a toad. It seems that if you
squeeze a male toad just behind the front legs, he will croak. A
female will not. Thus a toad in a pond in the middle of the night
can determine whether the other toad next to him is an
appropriate subject of his amorous attentions by climbing on and
listening. Apparently, it became semi-popular amongst some MIT
students to sheak up on each other & poke from both sides just
under the arms. Thus "no toad sexing".