  In a prior paper \cite{EFRST20}, two of us, along with P. Ellingsen, P. Felke
and A. Tkachenko, 1defined a new (output) multiplicative differential, and the
corresponding $c$-differential uniformity, which has the potential of extending
differential cryptanalysis. Here, we continue the work, by looking at some APN
functions through the mentioned concept and showing that their $c$-differential
uniformity increases significantly, in some cases.
