Cum ūnus ē custōdibus "Consiste!" clāmāvisset, alter fūr, magnā vōce commōtus, lāpsus est et humum cecidit.
custos, custōdis, m.: guard
cōnsistō, -sistere, -stitī, -stitus: to stop
alter, altera, alterum: the other
fūr, fūris, m.: thief
commoveō, commovēre, commōvī, commōtus: to move, upset
lābor, lābī, lāpsus sum: to slip
cadō, cadere, cecidī, cāsūrus: to fall