M3x4 bolt 'ejected' during print

After several prints and about 1 hour into the current print an M3 bolt has suddenly been ejected. I think it’s am M3x4 although I’m not sure of it is a longer bolt that has sheared.
It fell down from the front of the print area into the bottom of the printer.

As is will take some time to go through all the instruction to find where M3x4 bolts are used would someone be able to give me a tip? There are only 4 and I think they were in the printhead assembly, but I can’t see where one might be missing

Check the heater block and the pulleys?

Thanks but I found it, it’s the front left bed clip screw. I suspect the others may be coming loose to so I’ll check them all. That’s a relief…