ع (ʕ) and ح (ħ) — voiced and voiceless pharyngeal fricatives. Easy to confuse on hearing. English speakers tend to flatten both into a hint of h, or drop them.
ثلاثة — three. Two θ's framing the word.
ج ح خ share the same skeleton: a curve below the line. The dot above — or its absence, or its position — tells which is which.