  Numberlink is a logic puzzle with an objective to connect all pairs of cells
with the same number by non-crossing paths in a rectangular grid. In this
paper, we propose a physical protocol of zero-knowledge proof for Numberlink
using a deck of cards, which allows a prover to convince a verifier that he/she
knows a solution without revealing it. In particular, the protocol shows how to
physically count the number of elements in a list that are equal to a given
secret value without revealing that value, the positions of elements in the
list that are equal to it, or the value of any other element in the list.
Finally, we show that our protocol can be modified to verify a solution of the
well-known $k$ vertex-disjoint paths problem, both the undirected and directed
settings.
