  Let $(Z, D)$ be a pair of a smooth surface and a smooth anti-canonical
divisor. Denote by $\mathfrak{M}_\beta$ the moduli stack of genus $0$ relative
stable morphisms of class $\beta$ with full tangency to the boundary. Let $C_1$
and $C_2$ be rational curves fully tangent to $D$ at the same point $P$ and
assume that $C_1$ and $C_2$ are immersed and that $(C_1.C_2)_P=\min\{D.C_1,
D.C_2\}$. Then we show that the contribution of $C_1\cup C_2$ to the virtual
count of $\mathfrak{M}_{[C_1]+[C_2]}$ is $\min\{D.C_1, D.C_2\}$.
  As an example, we describe genus $0$ relative stable morphisms to
$(\mathbb{P}^2, (\hbox{cubic}))$ of degree $4$ with full tangency, and examine
how they contribute to the relative Gromov-Witten invariant.
