The "official" translation is "We are not looking at the last pear.", so while the variant with "watch" is accepted, it may be there just for the non native speakers (of which there are bound to be many, as English is the only available Czech course).
Because "to look for" means "to search", which is different than "to look at".
Look for - hledat Look at - dívat se
Different emphasis. Usually the most emphasized part is at the end.
"Nedíváme se NA POSLEDNÍ HRUŠKU." = 'We are not looking AT THE LAST PEAR.' (Because we're looking at the last onion.)
"Na poslední hrušku SE NEDÍVÁME." = 'We ARE NOT LOOKING at the last pear.' (But we're doing something else with it).