Souma is really susceptible to cracking up, and even memories will put him into laughing fits. But being self-conscious about this, he always tries to hide it. When he does this again at a clothing store his friend works at, the friend asks him why he does that, especially when it's so easy to tell anyway. Later, Shun also repeats the same sentiment...
When you laugh, I can't help but laugh too.
عندما تضحك، لا يسعني سوى الضّحك أيضاً
Aber nur, weil du mich angesteckt hast.
Es que me contagiaste la risa.
Es que me has contagiado la risa.
Votre rire est communicatif.
La tua risata è contagiosa, Haibara.
Não consigo segurar o riso
se você também começar a rir.
Потому что когда ты смеёшься,
мне не сдержаться.