EXPR is a software package for the recording and analysis of animal behaviour. Recording is done by pressing particular keyboard keys on the computer. The software then saves the sequence and timing of behaviours. Note that the DOS (1995: https://sourceforge.net/projects/expr/files/expr/fb-port-expr-00-1995/EXPR-binary-DOS-0.0.1995.tar.gz/download) version is currently the only fully functional and is recommended for use. On modern computers, DOS software can run in DOSBOX (https://www.dosbox.com/).